Oooh dear. That can be frustrating! For sure, make sure you are getting the pee spot realllllly thoroughly cleaned up, I love Nature's Miracle and similar enzyme-based cleaning solutions. If they can smell even a trace of old urine it'll encourage them to repeat there.
As for initial causative factors, there's always the possible medical route, a UTI or in older spayed females simple "leakage" but another thing to consider might be revenge peeing?
I don't have enough DS-specific experience, yet, so definitely interested in what others in the community might suggest, but I know GSDs, in particular can be notorious for revenge-peeing or using it to make a statement of displeasure.

Has anything occured recently to make her feel very put-out with you or someone at home?
My GSD, Cory, only used it on judicious occasion, she was impeccably housebroken and very proud of it, (even housebreaking Cedar for me when he was first adopted by scruffing him and dragging him to the door if he widdled inside!) but I can recall twice that she used peeing as a clear statement of opinion. The most memorable one was when I had first started "getting serious" with a long-term boyfriend... Cory was MOST put-out that he had usurped "her" spot on my bed, she squatted right there, on his half, all the while making full eye-contact!

"THERE! Sleep there, NOW, *expletive deleted*"
She did eventually grow to adore him, but that was a very memorable instance of peeing to make a statement.
I also had a friend whose sister had a GSD who, every time she went on a trip somehwere without him, would, at some point, pee in one of her left shoes. Always the left one.
Regardless of cause, you definitley can't let her continue doing it. Make sure to clean it really well, and maybe gate her out of that area for a while? If not incidents, slowly allow her more freedom, if she does it again, restrict access again for a while, maybe even go back to crating for a time period? Just a thought.
Good luck!