Rainbow System  -  she is not working with my schedule with my kids

My name is Nicole and I work for rainbow plus and when I got hired I told my manager I'm a single mom and I told her when i need off cause of my kids school and I give her it in Advance So she knows and she is giving me a hard time about it when I'm a single mom never had a problem with any of my jobs I have a babysitter I have to work around her schedule this is not fair this Thursday and Friday I have to do things with my kids at their school and my babysitter is going back to school so I told my manager that I can't close Monday Thursday and Friday she is giving me a hard time about it I worked retail before never had a problem they worked with me cause of my kids that's and she doesn't have help we'll hire more people I'm a single mom with no help I get help when I can