She has a long (what they call) "reinforcement history". This means, that management combined with positive reinforcement is about the only way to go, think of how one does this with a little puppy.

You never let the pup out of your eye. After max 90 minutes you take her to her pee-place but do not interact with her. (In you case, make sure that no toys are near or anything that would distract.) As soon as she squats to pee, whisper "pee" and when she's done, give her a yummy treat. Not just kibble, but something REALLY good, like a sliver of cheese or boiled chicken. Then you might play a short tug game or something she likes.

Scolding doesn't work. You've probably noticed this.

Also, where ever she's peed before MUST be completely cleaned with a non-amonia containing detergent. You can get this in a pet shop. The most important thing here is the management. If she CAN pee, she will. If you can offer her to pee BEFORE she get's the idea to AND it's worth her while to do so (getting a treat), then she'll do that.

Having said that, do have your vet check for any incontinence or any physical reason, why she can't hold it. Toy breeds cannot hold it as long as large breeds, but they should be physically able to hold it for 4+ hours, but they have to learn this.

Also, if she only does this when you're NOT home, this may also be a manifestation of separation anxiety. I didn't read in your question when she does this.