I don't think she appears until you've dealt with Benny (which might happen AFTER Ring a Ding Ding). Oddly, she always appears for me after taking House out of the equation, which makes me wonder why she wants to bother with bugging him. :shrug:
I think you're right about Benny.
In all three of my playthroughs, she's always appeared after I've dealt with Benny ... also, for me, she's always appeared as I'm leaving the Lucky 38.
Oh, and I think the reason she still wants the system bugged even if House is ... err ... taken out of the equation is because she believes his secrets can advance FoA medicine to help the entire Mojave wasteland.
That's my take on it, anyway. :shrug: