Regret

why would you discuss your DL behind her back with a stranger ?I had a difficult relationship with my FIL for decades but I would never have badmouthed him to any one else.If you have issues with her better to speak to HER about it than let someone else drop it into a conversation

I m with MOinca that’s what I’d do if it ever came back to you but unfortunately if your daughter in law did hear from the work colleague she probably wouldn’t say anything to you .....so just keep your fingers crossed nothing gets passed on
Nothing else you can do no point in working yourself up into a stew you can’t take it back just keep hoping the work colleague isn’t a gossip

In the very unlikely case of DiL finding out and telling you, deny it, say whatever you said, and you cannot remember what it was has suffered in the transmission. OK that will not be true, but better to lose a friend than a DiL you like - and remember you did say you got on with her.

I agree forget about it,the person you spoke to most likely has so please try to stop worrying.

Can you contact that person and make it clear that you do not wish that comment to be passed on to anyone, DIL in particular? That might set your mind at rest.

We have all done it!

I agree with Oldwoman. This was probably a 'passing' bit of chatter and unlikely to be passed on. If it were, don't forget your DIL probably also thinks she has a good relationship with you and would most likely view the 'messenger' as a meddler - as indeed she would be, if she were silly / insensitive enough to repeat something that common sense would say was a private matter. Try to let it go.

Unless the person you spoke to wants to cause upset they are unlikely to repeat what you said. I know all about saying something and then wishing I hadn't - but I think that the person you spoke to has probably forgotten what you said - we are the ones who remember and worry about it.