ease her into it without actually telling her you have a mommy fetish, or what rr/gfd are. things like:

"hey, how would you feel if i wore a choker?"

"can I be the little spoon tonight?"

"how would I look in a skirt?"

then slowly progress into more telling questions/statements, like:

"have you ever felt protective of me?"

(i sat here for 15 minutes trying to come up for another one, and have given up)

and then eventually when you're having a conversation with her, replace her name or the nickname you're using with "mommy". make sure to rehearse this beforehand so it genuinely sounds like an error on your part, and then frantically apologise, this has to look genuine like you actually did not expect that to come out and after having done it you wish to crawl out of your skin and stop existing. take every measure humanly possible to make this look as genuine as you can, i cannot stress that part enough. hopefully, she will be confused and ask you something along the lines of "what the fuck", and you can start gushing to your heart's desire as she will already have known

do not do anything i just said, i have literally never been on a date and i expect my advice is shit as a result