It could be a phase, but it sounds like your mil is having an impact. Can you ask her how she goes down for her day nap? If she is leaving her to cry it might explain some of the clingyness....?
I posted a very similar post in the last week or so! DS, who has been a fantastic sleeper, and super happy baby, has turned into a clingy, sooky baby, and needs rocking to sleep. He then wakes once a night and takes at least an hour to be cuddled back to sleep. For us, it does coincide with an increase in days at childcare (2 to 3), but it could also be a sleep regression or separation anxiety phase. DS is about the same age as your DD. Here's hoping its just a phase for both of them lol!
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