Strange Puppy House Training Behavior

I have a 15wk old Female French Bulldog who we have had since 8wks old. She is a bundle of joy and love her dearly. I'm hoping to get some advice on how to help her on her house training milestone.

What we have been doing:
1. Taking outside every 15mins or after naps, feedings, crate time, or accidents in house.
2. Gives treats after pee or poop outside and praise her.
3. If accident happens in house we show her what she has done and tell her no. Then take her outside.

After 7wks of doing this she still has many accidents in the house. She knows she is suppose to go outside because as soon as she pees (which she gives no notice) she will run to the back door which has a hanging bell.

What I find strange behavior for a female is walking/standing while peeing. She doesn't do this all the time. Then during playtime which we go outside before, she will pee while chasing a toy with a quick squat and then run. She will do this a couple times when we have her active in house for playtime which can range 30-45mins at a time. She has been tested for a UTI and its came back normal. When we have playtime outside we don't notice her relieving herself.

Water is offered from the time she gets up in the morning till 8pm. Bedtime is 10pm. She sleeps from 10pm-6am with no accidents.

I understand this will take some time as she is a puppy but I feel like she has not retained anything we are trying to teach her as she has always went to the back door after accidents. We think breeder had already started house training.

Has anyone done anything different that has helped with this milestone?