Interesting post and topic Ennie. Sorry you were uncomfortable. Here's a thought for you, it may sound extreme but I find it helps me. I don't accept treats or favors or anything from others unless I know them really well and feel safe and respected in the relationship. For me, trust is earned not immediate. That works both ways. I don't expect anyone to immediately trust me either. That's not the same as hypervigilance and living each day assuming that everyone is untrustworthy....I've been there in the past! That's no fun and not the path to peace either. At this point in my life, after having met so many different sorts of people I believe that most humans have good intentions. Most people are trying to be decent though they will make mistakes at times. And decent is very different from perfect The people with cruel intentions are an extreme minority of our species. That's my view though others don't have to agree with me

You had every right to decline answering the Q even though she treated you. That said, I completely understand your discomfort. Boundaries are tricky for most of us....I find them difficult myself particularly as I grew up in a family where the concept of a boundary was remote and nebulous at best!

I also recommend not speculating about why she asked the question/her motivation etc. It could have been completely innocent. Your title suggests that perhaps she only bought you lunch in order to pry into your personal life.
That would be a leap. People ask Qs for all sorts of reasons. Lots of people have asked me questions I did not wish to be asked....then when I gently said I was not willing to discuss that, they left it alone. It's rare that someone would keep pushing when we draw the line and if they do, then we have enough info to know that we cannot trust that person. Sorry if I misunderstood your post, just wanted to mention that she may not have had bad intentions.

As I said, it may help you to not accept (or indeed not offer) treats or favors until you have established your safety and respect in the relationship. I find that helps me. And yes, a treat is a treat...it does not authorize a person to pry