That is perfectly acceptable. Well, you know, some folks will look down on you for the antisocial bit of it (which is a shame, some people relish their alone time), but if you are doing it equally, no real harm done either.

And some folks will look down on you for being a female. Guess we are in the same boat?

Oh, I give them other reasons as well. I'm pretty quiet myself, I'm an immigrant, and my hair is blue. :D

Edit: I actually find the woman thing being the least of the problems now. It was a bigger issue living in the US than here in Norway, it seems.

Look at the context: what is a non obvious way one could help a female engineer? Mentoring them. That might include checking up on them eg perhaps by chatting over coffee. At the least, if you are mentoring male colleagues (even informally), you should try to give similar guidance to your female colleagues.

I don't care about your coffee habits. There is a conversation happening, and you're responding to only one part of it.

There's one coffee shop in my city where startup people just all happen to turn up at. I find going there by myself and just casually bumping into others throughout the day is nice without taking up too much time.