Ok, so that leaves me with having to create a game (normally idea comes first then I get people, this will be new) basically from scratch.
I need to find/create a world that will draw both of their interest.
Both enjoy Buffy the Vampire Slayer, and while I know the universe quite well, I don't know the RPG, which would leave me trying to GM (and teach) a system I dont know the first thing about OR shoehorn some other system into the Buffyverse.
I am.... "ok" when it comes to D&D 3.5 and I at least know the FR campaign setting reasonably well, however neither of them are even the slightest bit familiar with FR, and my GF has played D&D but doesn't remember what version (likely 2-3.5 but Its not clear) There is the question too on drawing in my 11 year old into a fantasy universe that she's never seen.
I haven't touched Shadowrun in nearly 20 years but the setting is a little more familiar (or at least accessible) to my tech-savvy daughter. But again, its a system I've forgotten most of, and no one else but me actually knows the setting.
I know Star Wars intimately, both the universe and the WEG version (and passing familiar with the Saga version) and my daughter is very familiar with the universe and my GF has at least seen the movies. (I like this option the best, but my GF is giving a little pushback so this may not be the best solution) I also have the most experience running SW. I think it also lends itself more to a 2 person campaign.
Other systems at my disposal but not really in consideration:
Vampire (too mature for the 11 year old)
Star Trek (no interest from anyone)
Battlestar Galactica (no interest)
Babylon 5 (No interest)
Firefly (Too mature)
I COULD Keep this simple and just basic 3.5 D&D and your run of the mill low level adventures until something strikes my fancy.
I COULD use 3.5 D&D and go the "magic starts working & tech all fails" from the year 2011. That saves me world building (at first) and might be more accessible to my (very bright) 11 year old.
Take a Avatar the Last Airbender, and use D&D 3.5 --make all characters Sorcerer/Monk types and split off only spells by element.
knowing my child, she'll do better if I can use either a pre-existing universe she's seen before and identifies with, such as (Avatar:TLA, Warriors, Star Wars, Buffy) than a homebrew or setting she's never seen (Forgotten Realms, Shadowrun, Firefly, etc)
Any ideas are welcome.