Oh *****! That is unfortunate but remember, you're not 18 anymore and you don't live in a small remote base.
You haven't seen her for years, she's not your friend, nor your husband's friend, and you don't need to have any relationship with her whatsoever.
If I were you and I did see her (hey it's probably unlikely) I would just ignore her, keep on walking. At most, if I was forced, I would say hi.

I hope you can calm down about this soon. I understand you don't feel comfortable with it. I live in a town where my 'ex best friend' still lives and I'm constantly worried about bumping into her.