I know I had my son at 18. I was to depressed to care for him, luckily my husband was a wonderful but overwhelmed father. As he got older I got healthier. Most people I know has children 1-2 years apart, whether overwhelmed or not. I don't feel if the baby is w. daddy there is any issue with her clubbing.
I have to constantly have to be on her to check on the baby and ask her to pay more attention to her Please stop doing this. It undermines her parenting, can cause her to see you less and hurt mommy and baby bond. She'll be a worse parent if she's second guessing everything. Really really have her look into an Iud or depo shot.