I'm thinking your best bet will be to go back to square one and essentially start over with the housetraining. Yes, she has access to the outdoors to pee, but she obviously doesn't realize that the house is off-limits for elimination. So, prepare yourself for a few weeks of keeping her constantly on your radar. Tether her to your belt with a short leash...dog her steps...whatever it takes to make sure that you and she are always focused on each other. Watch her for any signs that she needs to go and get her out immediately. If you catch her in the act, a guttural noise in the back of your throat to distract her while you pick her up and get her outside to finish. Praise her if she goes outside and especially if she asks to go out and successfully pees in the yard. If she still manages to pee and you don't notice till after the fact, just clean it up and forget it--correction after-the-fact does no good...
Also make sure you have an enzymatic cleaner formulated to eliminate urine odor. Regular cleaners clean it up enough to make it undetectable by human noses, but dogs can still smell the traces. Any urine odor remaining will actually encourage your pup to eliminate in that spot again. So a good enzymatic cleaner is a real help!
She'll get the idea--I think she just needs the training reinforced again. It happens--we've had a couple over the years that just took longer than the others. One of ours took 8 months. The good news is that the ones that are hardest to train seem to be the ones that are staunchest at eliminating in the proper venue when they get older.