I'm not sure either one of you were rude. As has been stated on this board before, it's not rude to ask, although the manner in which a person asks can be rude.
If she was demanding you allow her to register her people, and was being belligerent and talking down to you, then that would be rude. If she asked in a nice manner, there would not be anything rude in that. I think by your post she sounds like she was closer to the former than the latter, but I'm not sure she crossed the line.
I don't think you were rude. You cut her off to let her know you would not be able to accommodate her request. Stating the facts is not necessarily rude. So long as you did not yell at her, or call her names I think you are fine.