I think it's great that you can read her signals of being uncomfortable with being petted at certain times
She's a lucky girl, I come across plenty of clients who have no idea that their dogs are uncomfortable with certain things and just keep going.
I find often with TTouch bodywork you can find out very quickly which areas are more acceptable for the animal - in a different way than just stroking them, because often with stroking they will kind of put up with it out of habit, but TTouch is more like having a conversation with them as you listen and respond to their subtle little signals.
So to find out what areas she's happy (or not) with, what you could try is using the back of your hand/fingers, make a very light circular touch (you should be moving the skin rather than just going over the fur). Just do one circle and then move your hand to a different place (can be an inch away, so you can work in lines down her body, or you can just be random about it).
Watch for the following possible signals that she's not comfortable:
- closing her mouth (if it was open)
- holding her breath
- stopping and looking at you
- turning away from you or turning to face you (depending on her starting position)
- sitting down (if she was standing)
- if her eyes were nice and soft (with semi-closed eyelids) and she suddenly opens them
All those little signals are her talking to you and you can fairly quickly work out a kind of map of where she does or doesn't like to be touched (obviously move away from those areas when she tells you). You could then focus on petting her in the bits she does like (or if you wanted to work in a TTouch way you could pet the good bits but occasionally dip into the trouble spots - a quick stroke there then move back to an area she "likes").
Take lots of little breaks while you're doing this little discovery adventure with her, so that she knows you're not going to relentlessly keep fondling her
although tbh it sounds like you're already doing that really well already