My cousin isnt a very good mother. Help!

Okay so I expect some bad comments but really guys, I need help and advice! My cousin who is 22 has a son who is about to turn two and right now she and her son are living with my mom because her BD left her for a friend of hers (but she was totally cool with it they still stayed friends and I havent seen her show any animosity towards the father). So my mom asked her if she wanted to move in with her since the were literally living in a garage with like 6 other roommates (including BD and GF). When she moved into my moms house my mom started telling me stuff like my mom asked her if her son was up to date on vaccinations and she said something like when he was 6 months old a doctor "misdiagnosed" him with something so she never took him back! And my mom just texted me today and said that she never pays attention to him like she caught him eating lotion and toothpaste one time and when my mom told her what he was doing she laughed and said "yeah, hes a goat." And did nothing about it. These are just a few stories about her but I'm not posting to berate her I really need some advice on how to handle this!

I dont want my mom to just kick them out (she would never) because that little boy has no one to look after him! So what can I do to help my cousin learn to be a better mom without sounding rude or making her mad.