There are a few possibilities I see (and this is speculation):
1. Because you 'took over' with S5 when you were together, she is not used to having to do it alone and therefore calls to get your permission or acceptance on parenting him.
2. She may lack confidence because she wasn't previously given the mother role she wanted, so she is wanting to co-parent even though getting a D.
3. It may not be about S5 at all. She may just be using S5 as an excuse to call you and hear your voice.
I used to do that all the time before I learnt DB'ing, because I missed him so I'd talk to him about the baby or our 5 yr old so that he would have to speak to me.
