Yeah, heart icons are hopeless: as said above they are used for fitness apps as well as dating apps, but also by some social media, and even apps whose function has nothing at all to do with fitness or relationships but just because the developer chose that icon.
And that's not even a real notification icon, the photo looks like a lockscreen/always-on display, so from my limited experience of those I don't even guarantee how well it matches the app's status bar notification in appearance. The surround of that icon, which might be taken as a progress bar, suggests fitness app to me, but I can't give a positive ID.
Why don't you ask her if it bothers you?