Older dog, won’t pee on balcony. Pees on walks mostly, but in emergencies prefers rug to balcony. Advice?

I just adopted an older dog, chihuahua mix, 10 pounds. She's potty trained, and has demonstrated that at my parents' (who have a backyard) and at my downtown apartment. However, she also drinks a lot of water and has a small bladder. She ideally would pee every 1.5-2 hours. She holds it in when she's penned in the bedroom, but she sometimes can't make it down the elevator and outside.

I have a balcony, decent size, mostly surrounded by 3 walls and a ceiling though. Maybe it's because of that, but she won't go pee on the balcony. However she has twice peed on the rug in my living room. The latter time, we had just been on the balcony for 5 minutes trying to get her to pee, walked inside, and peed within a couple seconds (same spot). I have a reusable pee pad, and today I got an artificial grass patch and pee attractant spray. She has no interest. I have a fresh patch arriving on Tuesday.

I've now placed a pee pad over the area of the rug that she's already peed, in case she does it again, however I'd like to get her peeing on the balcony for the long term, since it's quicker and easier than going out, and currently she's also pretty nervous in the streets.

Any advice on getting her to go on the balcony? Does she consider it "indoors" since it's covered? Why does she prefer rug to artificial turf? I dog sat a dog in the past who also refused to pee in the balcony, who also had accidents inside. Never solved it. Really hoping that's not the case again, especially with how stressed the new dog gets in the streets.