I just needed a break

So my mom told me she was taking my girls on Tuesdays for a few months while she’s off and I’m at work. My husband has been deployed for months. I go to school and work full time, so naturally, I’m exhausted. I took off work one Tuesday to catch up on some sleep since my mom will have my girls. Well she found out I took off and told me she isn’t going to watch them. I’m kinda upset because like WHY? She knows I’m tired and overwhelmed, she knows my husband has been gone, and she’s the one who told me she would be taking my girls for a few months on Tuesdays! I never once asked her for help!