How do あなた deal with being forced to socialize with big groups?

I would ask your Grandmother for some 宇宙 if it's making あなた uncomfortable. I know she means well, but making it mandatory sounds like it's really stressful for you.

The only アドバイス I can give other than asking her to not pressure あなた with this every 日 is to try to focus on something that distracts あなた from yourself. Can あなた bring something like a game that everyone can play so あなた don't feel the focus is on you? If you're going out of the house, personally I find wearing sunglasses can help me feel like I have something to hide behind.

I hope that helped!