I understand your dilemna, but I dont think i could go along with that....first off, I really am turned off by 'registries' even for weddings, (i knwo i may be in the minority there, but i prefer the old fashioned notion of people being invited, period, and the recipients being grateful for their company and whatever gifts they may bring..)
so idea of a very wealthy couple telling people what to bring them for their second large house, is well, kind of sickening to me.
Its great you want to be friends and not let things go bad again, but i agree with a poster who said if you cannot tell her your honest feeling of being uncomfortable, it's not that solid of a friendship, it sounds more one-way to me.
I think a friendship built more mutually, with give and take and being able to appreciate and listen to a friends concerns is the only kind I'd want to begin with. Maybe the first step to having that with her is sit down, tell her how happy you are for her, and that your glad to be friends, and that you hope she will want to hear your thoughts/ feelings as well, then go on to tell her you would like to help with the party, but your personal philosophy is you don't do registries? That sounds more general,...it's just your policy in any social setting, not just hers, ?? That's the middleground i'd have to take on it..