Paying grandma to baby sit

Would you guys feel comfortable paying your baby’s grandma to babysit? My husband and I both work and prior to being pregnant my MIL was dying for a grand baby and saying how she would help etc etc. Well fast forward to 3 months post partum and she’s being annoying about baby sitting. I’m a nurse and have been a nurse for alll the times she’s known me so she knows I work 12 hours and don’t have a set schedule. She baby sits another child, and his moms has asked her to still be available 2-3 days a week. I let my employer know (by the way I started a new job) and they are accommodating but my MIL is complaining about my long work hours and she needs her money. I am doing my best for her to still be able to work, I don’t get more than 2 days off in a row because I have to work around the other moms schedule. My mom can watch the baby only 1 day a week. We offered to pay my MIL what she is making so she can stop her current baby sitting job. She gets paid $8 an hour and sometimes watches the 2 and 8 year old or she will go for only a few hours so it’s not a ton of money. Idk I’m just confused as to why all of a sudden she doesn’t want to help. She knows I just started a new job and I already had to ask for a weekend off so she can go to the beach with some friends of hers. I know she is retired and wants to live her life but she’s always gushing about the other boy she baby sits and seems like her own grand daughter is a chore.

Update: she was taking care of the other boy since he was 6 weeks old. She has worked holidays and last minute stuff for him but she makes a face when I show her the days I need help. I know the baby is my responsibility but she’s made it clear she would help to avoid a stranger caring for my baby yet still complains.