Many moons ago adopted a Sheltie that had been paper trained before she came to me. I was never able to get that dog to potty outside. She had the ‘paper potty’ so ingrained that she’d become very anxious and begin urinating immediately when I put her lead on to take her outside. That was an extreme case, of course, but what I’m trying to get at is that maybe your girl is having trouble understanding that it’s okay to potty on the balcony and outside as well. Maybe balcony train her exclusively, and once that’s accomplished, go ahead and go walkies and throw a praise party when she does her business. Patience and good luck!
P.S. A bit of grass sprinkled with the urine of another dog might encourage her to mark her territory.