Hello - sounds like you are doing a lot of good things in her potty training thus far. I adopted a 12 month old female Frenchie a few years ago and she had many accidents inside the house when she first came to us. We revisited potty training giving her a "refresher" and she has not had a single accident since. I have heard that Frenchies can be stubborn and hard to potty train. I know a few owners who have adult Frenchies who occasionally have accidents. Since it sounds like you are doing everything I would normally recommend already, the only thing I can think of would be to maybe select a high value treat or food that she absolutely loves and only give it to her when she goes potty outside. You indicated that you praise her when she goes outside, but maybe kick that up a notch too - like go crazy with excitement and pats and kisses. What happens when she does have an accident? It is best to simply clean it up if you discover the mess after the fact. If you catch her in the act, say a firm "NO!" and pick her up quickly and rush her outside. When she finishes there, do the praise. It also helps (at least for me every time I potty train a dog) to have the dog go in the same area every time and teach a command. This comes in handy for quick potty trips out during inclement weather. No one wants to stand outside for a long time if it's pouring rain, etc...so if you teach the "go potty" command and bring her to the same spot, she should go quickly for you. I no longer have to even say the command. She just knows we walk to her potty spot and she goes and we head back inside.
I wish you luck. I know it can be frustrating. Sounds like you have a really good start. If you think that it warrants a vet visit just to rule some medical issue out, go for it. If the occasional accident she is having follows a pattern, like if she squats to pee after rough playing/exercise, then you can head that off by taking her outside again right after you are done playing with her, etc. The general rule I like to follow is dogs should go outside to potty after waking up, after being crated, after rough playing, and of course after eating (about 30-60 minutes later).