It does happen. I have only encountered it once, and I continue to do so on
this web page
Others have tried at this site with the same message as a result: "The email you have provided is not valid". I've tried several of my other email identities - no luck. Having said that, this is the only site I've encountered with that problem, so that's no help in your situation. (The reason for my contact is to plead with them to fix their web cams which are frozen in the past).
To revert to
your challenge, I presume that it's possible to see on the site that the address has been identified correctly.
Is there some weird keyboard driver/type which has somehow found its way into the event?
Could it be that the @ character might be the culprit. Or could it be that none of them will accept an @hotmail address for their own reasons?
If she can try an email address with another domain address, perhaps that will work.
I'm puzzled too...
FOR