Three things:

One, there is significantly more toxic leadership in tech than in general careers. There are a lot of people who get promoted because they're intelligent and great at their job, but they have absolutely no leadership ability. Most of these people either fail completely, move along without issue, but quite a few get a chip on their shoulder.

Two, your teammate is a woman. Without even talking to either of you, they would pick her over you every day. Companies need to be diverse so they can point to their demographics if a lawsuit comes up. Unless you're a first generation black guy, her demographic status is far superior to yours. Also, if what I see on a daily basis is any measure, many guys are more receptive to women in a professional setting because they lack the ability to talk to women anywhere else.

Three, there is a possibility you're lacking in social skills. One of the things that always drove me crazy with younger new hires is their constant desire to be appreciated and get gold stickers. I shit you not, I had a kid who wanted to be praised just for showing up to work on time. Make sure you're not pining for compliments or praise. People who don't understand the difference between a career and playing pee-wee t-ball drives everyone crazy. Try to build up some resilience to what you find offensive. You made some good observations that will help you determine your future at this company, but nothing you should be overly offended by.

I say stick it out. The situation may change, and as a new grad it's going to be hard to find another job with only 3 months in. I always avoided people with short duration jobs because it typically meant they can't play well with others. I'd much rather have a team player who can't code for shit than an asshole coding genius. I can teach people how to code. It's much harder to teach them to be nice. Good luck.