I still wonder if someone has tried using tape recorder/video camera to get evidence on nasty in-laws/family members. Has anyone at all tried using these methods to prove to a non-believing husband the asli roop of his mom and siblings (in the event that they’re truly horrible people)???
Anyhow…Suhaina…if you don’t want to go, then is it possible for you to get your mom to go with your bro/sister to Pooh-Pee’s home?
Go to your Pooh-Pee’s home…get the sawab from Allah for maintaining relations with her. What goes around tends to come around.
Maybe the next time you visit Pooh-Pooh…and she makes those strange faces…just be a considerate **achi bachi **and innocently ask her, "Pooh-Pee…aap is tarha kyoon dekh rahin hain? Kya aap ki tabiyat to theek hai? Kya aap humain dekh kar khush nahin hain? Kya aap naaraz hain? Bataiye na! Hum aap k bhai ki family hain…aap apne bhai ko itna pasand karti hain…to bhai k family se bhi bahut mohabbat hogi… aur hamaray saath comfortable feel karna chahiye. To bataiye na, kya baat hai?? " 
^Make her feel uncomfortable for making those weird faces toward you.
If she has always been closer to your dad…then maybe she was JEALOUS/INSECURE from the day that your dad married your mom. Maybe, she thought that your mom (the bahu) was stealing your dad away from her. Or maybe she thinks that your family is better than hers. Who cares! Just be polite…and ignore her most of the time. Aik kaan k andar…doosray kaan se bahar. Aur agar thori si himmat ho…to kabhi kabaar…kuch chalak questions pooch liya karo…like the example I gave above.