How do you deal with it?

You are right just because you and your sister-in-law do not speak much is know reason for your friend to act that way towards you. You need to call her and see if you can go out and ask her why she is treating you this way. That is the only way you will fine out why she is ignoring you. She may not want to go out but you will know that you tried.

Ask her flat out what the problem is. You're right--it IS childish.....

I agree with you, your friendship should not be affected by your relationship with your sister-in-law...or vice versa, really. You might ask your friend if there is a problem between the two of you. It sounds as if your friendship may be suffering due to some adverse influence by your sister-in-law. If you value your friendship, you might have a heart to heart talk with your friend about your feelings and ask what's causing the sudden change between the two of you. Then get whatever it is cleared up. If it continues, you may have to choose between your friend and your emotional well-being. You have the right to feel good about yourself and your life, and if the change in your frienship/relationship is harming your well-being, you need to reevaluate that friendship/relationship. Best of luck to you. I hope it works out.

Everyone has differences. How does one live with in laws and not have differences. Not speaking to family, either it be your own or the one you married into, is just unspeakable. Life is too short to be so childish. Your husband and brother have to live with their wives not talking to each other. You dont have to agree on things or be bff's just get along and care about the spouses you married and their families. As for your friend, you need to ask her what you did for her not to talk to you or spend time with you. She can be friends with your sister in law and you at the same time. Be the bigger person and find out. You might find out it was nothing at all. The biggest mistake you can make is tell your friend to choose. That is never adult like in any way shape or form. Im sure you and your friend have differences you dont agree on so be the best friend, take her to lunch and find out what's going on. You might be surprised! Good luck!

Sorry to say but your good friend is shady. I don't know all the details but if you guys were friends before she became friends with your sister-in-law then shes the one in the wrong. If I was you I would just let it go because obviously shes missing out on a good friendship, and shes doing it in a childish way. I'm still in high school but I feel like I'm over people that act like that. I'm sure you have lots of better friends who won't put you through something like this. I know you and your sister-in-law don't get along but since shes family your going to be around her. I would suggest just trying to do little things together to try and reconnect on a friendly level, just something like getting your nails done together. Something simple, and something that just requires some small talk to get things better. You never know she might replace the good friendship you lost with the other girl. Just be optimistic.