AITA for telling my future SIL that I don’t have time to be her maid of honour?

I (25F) have been married to my husband (29F) for a few years now. He has a younger brother who recently got engaged. I have known his brother’s girlfriend for 4 years. We’re not extremely close but we hang out whenever there’s a family get together.

Anyways, for her bridal party she’s asked me to be the Maid of Honour. She has four other bridesmaids composed of cousins and old school friends. I told her that I’m very grateful that she has asked me but unfortunately I don’t have the time to do all the things expected of a MOH. I just had my first baby in November and it’s a lot. She has expressed wanting a bridal shower, bachelorette party, etc.

I told her I can just be a regular bridesmaid. She seemed fine but afterwards, my husband told me that she was venting to my brother and telling him that I’m being cold to her. According to her, she thinks I’m lying by saying I’m too busy because I’m on maternity leave and that I have “all the time in the world” and all her other friends work full time.

My husband agrees with me but his brother called me said I should try to “be accommodating to her”. I reconsidered and told her I would be her MOH if she covers half of the responsibilities, eg planning the bachelorette party. He said he would get back to me.

The next day, she calls me and asks me why I’m being so difficult. She says I’m the only one in the bridal party not working and that I should step up. I told her again that I’m on maternity leave taking care of a baby and it is actually even more demanding than full time work. She ended the call quite upset.

AITA for not being accommodating enough?