Am I reacting too harshly? Do I need to let this slide?

I have been dating my girlfriend for 6 months. She has told me she thinks she wants to marry me eventually, that I am perfect for her. She also has some depression occasionally where she thinks pretty irrationally for short periods of time. That is the back story.
I have been out of work for over a month and started a new temp job on Tuesday which I am very lucky to have. It is just a early morning (2 am early) stocking job at a retail store.
OK, so her and I had plans on Monday. She bailed to do something with a friend. A bit of a bummer but not that big of a deal I don't dwell on that stuff cause it's rare and stuff happens.
The next day, tuesday, she said she wanted to do something. I said, I would love to but I don't know how long I would be in orientation and since the very next day I had to get up at 1:30 am I need to sleep early, so I can't say for sure yes or no. While I am in this orientation she plans out all these things she wants to do. The orientation goes twice as long as I would have guessed. Til' 8 PM which is past when I wanted to stay up. I told her I was sorry but it was too late we should do it the next night. I needed to go home and go to bed. What happened next stunned me, I never would have thought she was capable of saying anything like this.

She got very upset and said "Well, if you don't want to be with me, I think I am going to go out to a party"
I said "It's not that don't want to be with you, babe, I just need to get more than 3 hours of sleep before my first day of work, I'm sorry, you never told me you had anything planned for us to do tonight until now. That's fun your going to a party, where is it?"
She said, "It's just a party downtown, at the bar, maybe I'll just go and have fun and drink" and she hung up. Confused, I tried calling her back and asking if she just meant by herself.
She said "I look adorable right now and I am feeling very sexy and adventurous but since you don't want to be with me, maybe there will be someone who does think I look cute and wants to be with me"
I said " You mean like another guy?"
She said "Yeah" very frankly.
I said "I want to be with you, I can come see you if you need me."
She said "No, your sleep is more important than me, apparently" and hung up.
I tried calling her back a few times, she finally answers and says "What"
I start trying to talk to her and she says "My co-worker Colby is on the other line, I am going to have to call you back"
She calls me back a few minutes later crying and saying she is so sorry, she doesn't know why she said that, she didn't really mean it, she knows sleep is important and that my job is important. I told her what she said hurt.
She said "I'm so sorry, I was being very selfish, and overly emotional and irrational, please forgive me"
Then she said "You know I would never do anything like that. I wasn't really going to do something with him"
I said, "Him?"
She said "I mean, him as in some other guy, not anyone in particular."
That sounded fishy, as if she already had someone in mind. Then she said I should go to bed and I did, sort of, I didn't sleep

This has been eating me up ever since. I tried discussing it with her and she says she is so so sorry, but I should not be worried and that she apologized, she said she said it at an abnormally emotional time, I just need to forget it and move on.

I am afraid the next time I am not able to drop my previous plans to make way for her plans she will actually do something and I will be much more hurt.

That's my spill, sorry it's long. I just feel lost, I believe in forgiving and that you should not hold things against people to hard, I have put behind many thing she has said that are not so nice that she has said during these emotional times, but this just seems like sticking with it means I will be hurt in the end. Thanks to anyone who reads and comments.

move on. She is already exhibiting manipulative behavior. It will only get worse with time

Hmmm...ok as opposed to just saying "move on".

Sit down with your girl and have a mature talk about this TYPE of behavior. Put your foot down that you won't stand for it because you don't play that childish game with her and that you will take any indicators of her "going after other guys" VERY seriously as grounds for breaking up. If she is going to try manipulative tactics, you have to be a man and out your foot down on it. Act stern but understanding towards her because of her depression. You have to set ground rules and lines that you won't toy with, it's important and a respect thing.

On top of that (I dated a depressed girl...ugh, it can be a pain...same thing as you - mood swings), tell her to LET YOU KNOW when she is "feeling down" and discuss what is best for YOU to do when she is (go home, don't bother her,talk it over, etc.).

She wasnt thinking... Although it was manipulative, I doubt she wanted to really go out and do those things, she just wanted your attention. I dont think you should have to put up with it though. But you never know, she may feel really horrible about it now and really wont do it again. I'd worry if she shows signs of this behavior again, but if she has only done this once, I think she deserves another chance.

Might have stemmed from insecurity and depression. She was being a little selfish too. It was OK for her to blow off your plans for a friend a few days earlier but when you blew her off for some much-needed sleep she snapped. Good for you for not throwing that comparison in her face, I would have had a hard time refraining myself!

So, she made plans without thinking about your sleep schedule, got herself all dolled up, was all set for a great night out with you and then got shot down. She didn't think, she just lashed out at you. It's NOT OK to threaten you with cheating though. And you played right into it by doing an about face and saying you'd be right over if she needed you, etc. That only teaches her that making you jealous works like a charm!

Sounds like her coworker Colby may have pointed out her bad behavior because your girlfriend was all apologies when she got off the phone with Colby. I think that sets the stage for a calm discussion about how you'll handle things in the future if one of you feels let down by the other (careful to make it about both of you, not all about her). Encourage your girlfriend to share how and why she feels hurt and see if the two of you can come up with a solution that will make you both feel good about things instead of her playing the victim.

I know depression can be a pain, I have lived with it for years now. It's better now than it was but trust me with my ex I had it really bad, probably one of the worst cases I have seen, at doctors every week or something. Anyway, using depression as an excuse for mood swings is so easy, yes depressed people do get them but not like she is making out. By the sound of it she is feeling down or insecure about something and instead of talking to you about it she is trying to make you jelaous and seeing if you would drop anything to go see her. I done this a few times and my ex did, TBH I wish he didn't I wish he put his foot down and told me to stop doing it and just talk about things. I would have respected him more doing this rather than jumping at everything I said because I was 'depressed'. I do suggest you talk to her properly face to face. Tell her that you know it's hard to have depression and that you will be there to support her when ever she needs it but you wont put up with her treating you this way, tell her you would rather she talked to you even if she thinks it might hurt you. Trust me it's better you get her to talk about things rather than her doing this too you. Hope things get easier for you. x