Is it wrong to leave a 5 week old with her for a few hours

My mom is treating me like I'm a horrible mother for leaving my daughter with my ex for a few hours. He's a good dad and she has no reason to think otherwise. Is she overreacting or am I really a horrible mother?

Edit: yes he is the father and we only recently broke up. He was there when I gave birth but things are just not working out so I left him. He sees her all the time but this is the first time he's watching her alone. We live less than 15 minutes away from each other and we communicate well with each other still.

Btw this is the first time I've left her alone with anyone. I'm with her literally 24/7