Some good thoughts here, thanks, although there are also some things I don't agree with or just wouldn't work for my situation, but I won't do a blow-by-blow.
One thing that quickly became clear from reading this thread is that the details do make a difference. I mean, as a general rule I would always be open to having someone new try the game out, especially if I was looking for more players. But let me add some details into the mix:
1) She has no interest in joining as a regular (afaik) and probably couldn't because they have a baby and we rotate where we play, so unless they brought their baby (which would not be ideal) they couldn't both play.
2) Not including myself, there are already five regular players and two who are on the verge of joining--and that doesn't include this spouse (or other Curious Spouses who want to give it a try, and there are one or two others!). In other words, we're already bursting at the seems for how many I feel comfortable DMing.
3) One of the above mentioned new players may be starting during this session. So I am going to have two new players in this session, neither of whom I know well.
I did end up inviting her because it seemed like the Right Thing to Do (I don't know her well, it is the first time I'll be at her house, etc), but if I'm honest, given the above circumstances I'd actually prefer if she didn't play. But when I make a choice like this I will welcome her with open arms and hope she has a good time.