What goes through a girls mind when she says she needs time???

So me and my girlfriend got into an argument which led her to need time to think over our relationship. She was extremely hurt and very dissapointed.... She said she didnt want to have a future where all we did was argue...
Its been a week since she called me, so i called her today and she said that she really needed time because she didnt wanna say anything she didnt mean because she was upset, and i know girls say things they dont mean when their upset.
Our argument was a misunderstanding about me coming down for her birthday which led to her thinking that i dont try in the relationship due to me not calling her back when she hangs up on me when we argue and that i only tend to apologize when i see her cry and she is worried that i would do the same thing in the future. But i NEVER intentionally do it on purpose but i know i do it, and its something i need to work on...

I can tell shes still very upset about our argument. She said for me to not call or text her anymore until she clears her mind and knows what she really wants.

She said some cold things that hurt when i talked to her, and she knew it but she said she was upset so i can understasnd her saying it. She just says she really needs time and she doesnt wanna do or say anything to ruin the relationship at the moment because of her being upset. She is also going through some stress with her business as well.

My question is if i leave her alone will her anger/sadness subside? Do girls miss their boyfriends after a while of no contact???

additional info: we been together for 3 years, talk about marriage all the time, planned our marriage, told her parents shes gonna marry me etc... i know we both love each other so much, she means everything to me and so much more....

i just need some insight on my situation

Her feelings may or may not subside, but that's not really the issue. You should leave her alone because she asked you to. Contacting her against her wishes certainly isn't going to help the situation. You're going to have the uncomfortable task of sitting and waiting. She'll come to you when she's ready.