4.5 month old peeing upstairs

Hi, we’ve had our puppy for 1.5 months. She’s a black lab/AmStaff mix but there’s a good chance there’s some pit in there, too.

She has downstairs and overnight potty training down pat. Downstairs she rings a bell to be let out. Overnight we originally had her crated but lately she’s been sleeping in our bed. In the morning she goes straight outside. No accidents.

Here’s the problem: when I’m going about my day if I have to be upstairs I let her out, she goes, then I leash her to me and we go upstairs. And… sometimes within minutes she pees up there!

Do I crate her while upstairs? How do I proceed?

Thank you for your advice!