I've never asked for a beta reader. I used to beta for a German friend, but frankly, her comprehension of English was absolutely superb! Better than most English speakers, that's for sure. But I don't think she really appreciated how good she was, so there was usually little for me to do with her stories. lol She didn't even speak English with an accent, which is remarkable. Anyway, I think someone DEMANDING that a character be changed to suit the would-be beta reader is ludicrous, and they clearly don't understand the point of being a beta reader. If the beta reader feels major changes need to be made then they can suggest it, but ultimately it's 100% up to author, since it is their story, after all. I know I've had reviews suggesting things that would have utterly changed - and ruined - the story if I'd followed their advice, which showed they clearly didn't get what I was saying. At least your friend had the sense to tell this person to hit the road.