I think mentioning that your mom worked is a great idea! Also, maybe try to point out that though you can tell her child is always happy to see her when she gets home, that she has a great time throughout the day too...obviously only say that if it's true which I am hoping it is
I've worked for a mother that would text me hours after she left thinking her 2 year old would still be crying about her leaving. I had to reassure her that the crying stopped within 3 minutes of her departure. Sometimes I felt bad making it seem so simple because I felt like maybe she was missing her son more than he was missing her so I would highlight how excited he gets when she comes home and stuff.