Hi JamesR,
That's an interesting story. I think you may be on to something here. I shall attempt to answer your questions as best I can.
1) I would say she is definitely more likely to accept it. Sadly there can be no guarantee about such things but I'd say she's most unlikely to freak or consider a diaper fetish so waaay out there she can't deal with it.
2) Me personally yes, I definitely would risk it, but thats just me (my best friend already knows). The subject of coming out or being outed to friend comes up here a lot, and the advice always given is "look at what you hope to gain, and what you risk if it backfires, is it worth it?". As everyone's friends and circumstances are different, only you can decide if the risk is worth it. From what you've written though, she doesn't sound like the type who would blab something like that - I'm sure she knows how that feels herself in her line of work! And if your buddy dated this girl for a while, surely he's relatively open minded himself. Anyways, that ones up to you
3) You've already taken the first step and told her that there is something, and she wanted you to tell her more. Considering how open and frank she has been with you already about her work, I'd say tell her as soon as you feel comfortable with it. As I said above, I doubt she'd freak, worst case; she tells you she's not into it and doesn't want to try it. Although much like 2) this is ultimately a judgment call only you can make - but what you have written sounds promising at least
4) Keep us posted how it goes, and best of luck!