I see this is your first post, welcome to the library!

I remember for sure that if someone has passed out, they've already got brain damage happening.

I like this sort of play too, albeit it definitely is one of the more dangerous ones and it's good that you're asking for advice and resources. I'd say also make sure you determine a non-verbal cue to stop.

If she has little red dots around her eye area the next day then she has burst blood vessels around her eyes and they should clear up in a few days. You can get this from being asphyxiated, hanging upside-down and vomiting too hard.