Feeling like the worst mom

I am a mom of a 2 year old and she is my world. I would spend every second with her if I could but my family is reliant upon me working 40 hours to cover the bills. I also go to school 2 hours a week to try and better myself so I can get a better paying job. This all requires that she spends a lot of time with my mother and grandmother. That would be totally fine except now they are so close my daughter wont always want to leave and will cry to stay at their house. It kills me inside because I wish I didn't have to be away so much. She is such a mommy's girl and I know she loves me but when I go to pick her up and she cries like that not wanting to leave I can't help but feel like I am the worst mother in the world when I am just trying to do my best for her. I hope one day she will understand why mommy has to be away from her and that it is all for her.