I'm confused by an exes behavior

Short Synopsis
My ex broke up with me just over a month ago via text message. (We dated 15 months) I resisted at first but she firmly stopped my gestures. I finally told her I agree, the break up is for the best. A week later I got an email, telling me to stop calling people about her. (I wasn't, a misunderstanding) which led to some nasty emails back and forth until I finally blocked her. (I didn't take any cheap shots in my last email)
It was very difficult for me, a new experience.
Anyway, 3 weeks passed. I was feeling good, so I decided to send her a friendly email because it ended so badly. ie blah, blah how are you, hope there still isn't any resentment.
I was expecting maybe a block, or no response but hoping for a friendly "I'm doing good, sorry it didn't work out, I've moved on" type
Instead, she responded by saying, actually there is still a lot of resentment, gave me a low blow. And proceeding to tell me how she is doing "really well" and added that she is on vacation at a cabin that "puts mine to shame"

Anyone seen this type of behavior?
I was the one who was dumped, through a text no less...

She's acting like a child. If she can't say something civilized, its not worth it. Its over dude. let it go.

yeah, I know it's over. I swallowed my pride in an attempt to be decent. Why does she still feel the need to take cheap shots, and reaffirm how much she doesn't like me? I didn't say anything remotely close to wanting her back or missing her in my email.

That's because you know how to act like the bigger man while she's still putting her tongue out to spite you.

[edit] If she can't be more civilized and mature towards you. better to walk away than indulge her childish behavior. you get nothing out of it and it would start to feel like that little piece of meat that gets stuck between your teeth. the more you suck at it, the deeper lodges in between and more irritating it becomes.

Well, that maybe. She was always very into me. Just a couple months before the breakup she spent a lot of money on things for my apartment, gained 40 pounds, then broke up with me... Now this.

All very strange behavior

No use trying to understand her. Her childish mentality will only make for a frustrating series of attempts at finding a path through that maze she calls her mind. Just understand that she's changed (as people do) and you are no longer a part of the equation. It's a harsh reality to face, but better you face it sooner than later.