No, actually that would work. I'd add tho, did the kids see her, as well? If so I'd say, the kids saw her first and you realized etc.....could follow thru with noting that walking is great exercise, as long as it isn't raining! etc....just to get it started. Unless she is a dud, she can take it from there, and next thing you both know, you're talking.

If the kids didn't see her, then mentioning you did is fine...just make sure it sound sort as a btw...and 'you must live close' and if she smiles or at least keeps attention on you, go for the rain thing.

I know you can do this!! Just showing you've noticed her outside work would be flattering. Build on that.