Re: What are you doing?
It's just a variation on a greeting. I know lots of people who do it. It isn't an attempt to invade your privacy.
Every time she says it, just say "not much" and move on.
I had a boss once who would instantly fire people if they said "Not a problem" or something similar when someone said "thank you". The only thing acceptable to say was "you're welcome". Honestly, it can really be a regional thing. Where I'm from, unless it is a very professional serious relationship, "no problem" is not even just acceptable, but it's considered more personal.
I once asked him how long he would last if someone fired him the minute that he said 'y'all' instead of the less Southern variations - since most of our clients were in the northeast. I don't work there anymore.
Anyway OP, relax. If that's your biggest problem you are doing great.
Don't let people become a priority in your life when you're just an option in theirs.