Am I obliged to help my sister-in-law with her bridal shower ?

[broehain61]

My sister-in-law is getting married next year. She has asked me to help her with some things with her bridal shower. I am not the one throwing her this shower but she is seeking my help. The twist in the story is that for last three years, she has been a horrible person to me. She holds some grudge against me (which I still don't know what) and ignored me on all family functions. Once she told me I suck and I should not be surprised if people hate me. She even came to my house and did not talk to me. Truly mean and selfish.

Fast forward to now where she has a "good" life and all the things going for her so she no longer hates me (or atleast pretends infront of her fiance). I have a newborn and I am really not in a position to run around and do "shower" things for her. I am super busy with my baby. I mean, if I reeeeeeeeally wanted, I probably could bend backwards and do this for someone else but my heart just doesn't want to do anything for her ........ How do I get out of this politely ?? In reality, I want to tell her to take a hike but I am a "reasonable" person who chooses to be civil in such relations for the sake of the family peace. Please help !!!