Posted by Double M
If your girlfriend's mom doesn't like you, the entirety of your relationship with this girl is not going to go well.
In most cases, Moms hold crazy weight over their kids, even when the kids are grown. You may not think this matters, but when it comes to girlfriends it matters a ton.
If your girlfriend's mom doesn't like you, she will do everything she can to make it hard for your relationship to make it. In high school, the curfew gets strict, family-only dinners become more frequent, and money to go to the movies or shopping suddenly dries up. Basically, nothing will be easy.
This stranglehold might loosen as the daughter gets older, but it can still bite you. When you get in a fight and your girlfriend calls her mom, guess what happens if her mom doesn't like you? You get a deuce dropped on you whether you were right or not.
I'm not saying you just need to run if the girl's mom doesn't like you, just that you need to put in some effort to make sure she does. Say the right things to her, be polite in her house, and don't give her any ammo - especially in the first few months - to not like you.
If after all that effort your girl's mom still doesn't like you, then know that you'll be fighting two (or more, depending on her sisters or friends) women everytime you get in a fight or have a disagreement over a simple decision. Then, unfortunately, you have to decide for youself whether it is worth it.