Don't let anyone including your gf pressure you into doing it before you're ready.

Her biggest deal is that she “doesn’t want to be pregnant walking down the aisle” or have the baby born before the wedding

Well shit. It was an unplanned pregnancy, that happens and she needs to understand that. Pregnancy doesn't magically make you ready for a wedding.

It’s just annoying I feel like I have little control over this whole marriage thing and if I bring it up my girlfriend immediately starts saying “oh fine well I’ll just not bring it up anymore” and getting really butthurt

You do have control, if she wants to get buthurt fine.