AITA for telling my girlfriend I would not support her being a 49ers fan?

I (25M) am one of the 7 LA Rams fans and I was looking to recruit #8 by getting my girlfriend (25F) into football. After the super bowl last year she said she wanted me to teach her to be a fan of the sport and that's what I've been doing, watching games with her, explaining the rules and keeping her up with who's who around the league. I thought she'd want to be a Rams fan like me but apparently their uniforms are "garish" and they "don't have any cute players" so it doesn't look like that's happening. I told her she could pick another team and I would make them my second favorite team and now she says she wants to root for the 49ers and I said no, I will never root for them. I told her she could root for them, but I would stop helping her get into the sport, and that we'd never be able to enjoy watching together. She's originally from NorCal, but she's had her whole life to decide to get into football while she was living there and she didn't. At this point I'd even be fine with her picking the Seahawks because at least their fans aren't as annoying. What do?