Crying Relapse... Not sure what to do..

So I have a 1.5 year old girl and her 2.5 yr old sister in my care.

I have been having issues with the 1.5 year old crying.

When we go for quiet time she cries for at least 10-15 minutes u til she falls asleep only to wake up 30-45 mins later and continue crying.. I Di put quiet things in her play pen for when she wakes up.. Her diaper is also changed and if she has a poop I change her right away so that's not the issue.. Maybe it's teething I'll ask mom tonight.

But the thing is she was like this when she started 2 months ago, but after a week and a half she was great. A perfect napper went down good no tears or anything..
And also lately whenever her sister goes to the bathroom ant somewhere her little sister isn't she starts crying..

I don't get it I thought she liked it her. She never used to cry so much??

Thoughts??

Where do you have her sleeping? I would try the room darkening blinds/curtains and a white noise machine for her. If she wakes up at the 45 minute point go back in lay her down, ssssh her and leave the room and leave her in her playpen for the remaining nap period.
I have one in my care who is 16 months, she recently started waking at the 45 minute point then crying for 15 minutes, falling back to sleep then waking up again. I will go in once and lay her back down but then she stays there for the remaining nap time.

I agree with above. Lay her down, don't change her and leave her.

The wanting to be with her sister. I wouldn't take that personally. She is young, her sister might make her feel safe, it could be a phase.

The wanting to be with the sister is a security thing and can be the oldest with the youngest as often as the youngest with the older one. They are using the sibling as a substitute for mom. I have had issues with siblings this way when putting the one group ie the older ones in the kitchen to play a game or craft and kept the younger ones in the play area next door or had to tell an older child to go play and leave the younger sibling alone to do their own thing that their job at daycare was not to be at the beck and call of the older sibling.