Thanks for all the replies ladies..
Her bed has 2 mattress protectors so her mattress is staying dry but her sheets are getting drenched.

The long bonds suits would probably be the same situation and be too hot for her to wear them as summer approaches. I've tried the short sleeve ones but she pulls those undone in no time at all.
I've already tried the pull up idea and she pulled that off just the same. I've also tried putting her potty in her room and explaining to her that if she wants to sleep with no clothes on that she has to get up and go wee wee on the potty - no good though..