Thanks everyone I really appreciate your replies.
I think I will cap the nap at 1.5/2 hours but by the sounds of it, and as I suspected, it's behavioural.
Malls he wanted tonight was to be cuddled to sleep. She had always hated being nursed to sleep but I'm guessing she sees DS on my chest a lot and gets jealous.
I'll do it for her if that's what she needs and sounds like we just need to ride out this period.