Friend's fiancé on dating site.

I don't know what to do. I work with a girl and today while I was swiping I saw her fiancé on a dating site. I'm not really close to her but we are associates. We go to lunch from time to time and have even went out for a night of bar hopping but I don't consider her a friend. I'm not sure if I should tell her that I saw her fiancé or not. They just got engaged 2 weeks ago and are planning baby #2. If I tell her I'm not really sure how I should do it. I would want someone to tell me if they saw the man I loved doing something like this but not everyone is the same. I don't want work to be awkward if she ends up being upset with me. Should I say something? If so, how do I say it ? 
Please help, she has a big heart and I don't want to see her to get played.