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.
"There's an end to every storm. Once all the trees have been uprooted. Once all the houses have been ripped apart. The wind will hush, the clouds will part, the rain will stop, the sky will clear in an instant. But only then, in those quiet moments after the storm, do we learn who was strong enough to survive it."
-- Meredith Grey