When they add you, you have to accept them too, so you must have done this at the beginning and allowed her onto your site.
Cant you just delete her off your/DD facebook? I have a cull every so often on my facebook and also dont accept everyone who wants to be friends with me.
I deleted my AH (not estranged and still married) from my friends list a few months ago and he still hasn't noticed!! I got a bit fed up of the drunken comments he was leaving on our joint friends posts (not regularly) and this way I dont have to see them, so they dont bother me anymore.
Its your facebook, so do what you like. If your Aunt doesn't like it - tough. She cant make you be friends with her, its your page. Whats the worse that could happen anyway? I am betting she will move on pretty quickly.
I know co-dependants (I'm one) struggle with worrying about what people think of them when doing certain things, but really - deleting her from your facebook friends is not one you should worry about and its so easy to do with the best outcome for yourself/DD. Be strong, be brave!