My DD is almost 4months too, and her day naps have changed. She used to sleep for 2hour stretches, every 2/3 hours during the day. Easy peasy.
Now she has three 30min naps and then goes down for the night at around 7pm.
She no longer simply goes to sleep on her own for any of these sleeps.. I find I have to cuddle her, walk around.
Here's a trick you may not have tried: Sit on your bed with your legs straight in front and place a pillow on your shins, and let her lie on it, and shake your legs from side to side till she falls asleep. I read a book while doing this!
I have found also that when she really doesn;t want to sleep, I realise that she's hungry..AGAIN. So your DD may be going through a growth spurt/developmental milestone.
Oh and I don't feed play sleep anymore.. Sometimes she's just not interested in feeding when she wakes up, but loves a nice relaxing feed before bed!