[HELP] Female dog pees on bedding!?

1 year old Pit/Boston Terrier, spayed female. I’ve had her for 5 months and she never had an indoor accident, but just this month that changed. First she peed while sitting in bed next to me in bed. I didn’t even realize because she was just laying down normally. Then we went camping and she was sleeping in the tent. We were literally OUTDOORS and she peed on my bedding. She often lays on my pillow; today I went to lay down and she had peed on it.

WHY does she do this? How should I treat this issue? Her past is mostly unknown as she was abandoned at a shelter.