Hi there, welcome
So, if she was born May 29 that puts her at about 7 months old, so she is now a hormonal teenager. Couple that with moving to a new home, and I’m guessing that explains her loss of box habits. It’s pretty normal for new buns to take a bit of time to sort out their potty spots in a new home.
I do think it would be good to wait a couple weeks for her to settle in, but spaying should help! I’m guessing the old owner didn’t have this problem simple because she hadn’t hit puberty at first, and there weren’t any big changes to trigger the marking.
What type of flooring does she have in her pen? Any soft flooring can confuse them a bit (as you saw with the soft blanket). Some buns also are encouraged to use their box with soft bedding, like care fresh.
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The answers provided in this discussion are for general guideline purposes only. The information is not intended to diagnose or treat your pet. Seek the advice of your veterinarian or a qualified behaviorist.