YANBU but do leave room for it being entirely innocent. She could have just been feeling elated about how well her job was going, in a good mood, and wanted to express genuine appreciation for your husband. It may not have meant any more than exactly what was said.
Not everyone has wonderful social skills, or understand what others may read between the lines of what they say, or understand when a message of appreciation is inappropriate.
This sounds like the kind of mistake I'd make, if I allowed myself to message/communicate with people (which I do not, for this reason). I say what I mean and never intend for anything to be read "in between my lines", so have realised I often put my foot in it when people derive meaning from my words/messages that isn't there. I have made people uncomfortable in the past, just trying to be kind. People make shit up from my POV... But then I remember, that many people do have ulterior motives behind their words and do intend there to be meaning inbetween the lines, and so people assume I'm the same. Then it makes sense.
Just leave room for her being like me and not intending anything by it other than what was said, rather than like you.
If your husband is uncomfortable though, he should tell her or HR, so HR can tell her. If it was just an innocent expression of appreciation, she might not realise it makes others uncomfortable.
She could also be a homewrecking cow of course. Just wanted to give a different perspective, just to remind that all sorts of people exist and not everything is a drama.