Mother in law requesting big birthday party

My mother in law is requesting a big party for her 60th birthday. I know she’s super excited and all but she wants her kids to pay for it. 2 of my sister in laws are SAHM moms plus myself (married to only son) and 2 are underage. What she’s requesting is too much but she’s the type of person to stop talking to you for as long as she feels necessary if you go against her. My husband wants to contribute but we can barely afford to pay our bills. I’m hoping to start working at the start of next year but idk if I’m willing to contribute when she doesn’t even bother calling to check on our daughter.

My 2 sister in laws have 3 kids and each and are struggling already. I just don’t think it’s fair. She has her husband and 1 of her underaged kids works part time and she feels obligated to contribute. She wants to invite 60 people and have a mariachi band. I don’t think it’s fair for her to ask for this knowing her kids are not in the best place financially but if we don’t do this she’ll ignore us for months.