Imho, the collar pop has to happen before the lunge, when her muscles tense, forward shift in weight, ears tuning in etc. Maybe you are focusing on what she is looking at rather than what her body is doing thus missing the precise moment for a correction. It took a while for me to understand my boy's body language but once I did, catching the "I'm about ready to react" body language stage required a lot less collar pop force and more willingness to comply with my directions/commands.
Fwiw, once I became really in tune with what his body was telling me and also the clarity of what can be expected if he did this rather than that, it became a lot easier.
Ultimately, I wanted him to be able to make the right choice on his own. It is achievable, but it does take understanding and communication between you and her.
I would also pair a food reward with verbal and touch praise. A scritch under the chin or behind the ears, any sweet spot she has for good behavior. This will help the "feel good" hormones kick in. This last sentence is just my own theory but that's what I did for my boy and it seemed to help a lot.
Just giving some personal info concerning the prong while we were working through his reactivity.
Keep at it, find a trainer you trust, pay attention to your girl as she will tell you what methods work best for her as it will be the method that gets her to behave appropriately with out dousing her spirit.
"If you can't see his soul when you look in his eyes, then you need a seeing-eye dog"