I put her inside her playpen today afternoon and I’m planning on letting her sleep there for today, and see if there’s any difference.
That’s a good idea. So with the litterbox still in the cage bottom? Or out in the pen?
One thing to try is leave the cage top on but a door (or 2) open. Perhaps she likes having something overhead that gives her a sense of security?
If the cage is a top opening one, you could try adapting a box to fit over the top instead.
I really don’t know if this would make a difference but worth a try right?
What type of flooring is the play pen set on? If wood/vinyl/laminate etc, try putting a mat down near by the cage or litterbox. So she can jump in and out without losing her footing.
You really needn’t worry about her holding on affecting her health. She’ll have to go at some point. It probably is like Baxter n Boo mentioned, she just goes at certain times. She could be very efficient in her routines. I notice some of my buns hardly drink water and urinate infrequently. Then I have a couple that are the opposite! Most of the pooping happens when eating their hay in the litterbox. Sometimes it’s a ton all at once.
I know it’s hard to leave your bunny. I remember feeling so anxious the first time I did when I had just the one.