have her eat something oily beforehand. i would say just take a sip of olive oil beforehand, but many people don't like the taste but the oil will make is easier for the throat to relax. don't know why, but it worked when i tried it
I have read your other post about this subject so here is my suggestion. Have her start the first few times really easy at first. And no pressure for her to do much of anything. Just a little bit with some kissing and a little action on just the tip. Then as she becomes more comfortable she can work up to more. Maybe also get some chocolate (my favorite!) or something else to place on the end to make the taste a bit better (nothing personal to your hygene or anything) that may be part of the problem of her gagging. Good luck.
I think the best way to prevent it is to not swallow! Sometimes I can swallow it no problem and other times I can just tell that I'll gag if I do. So, when I can't swallow it I just politely go to the bathroom and spit it out. It's the same result either way!
If you go to an adult book store ,via in person or online ,they sell little "melt in your mouth" (sort of like those new breath fresheners)candies that can help to numb the back of your throat.They also are kind of minty..