Would you tell the mom if their kid steals?

The hockey season has just started at school, and Little Miss had her first official hockey lesson yesterday. We had to go and buy the mouth guard as well, as they are not allowed to play if they don't have one.

When I went to fetch her yesterday, she told me that her mouth guard was missing when she had to get dressed for her hockey practice. She saw that a friend of hers was running around with one that looks exactly the same as hers. She told her different stories about where she got it from. Since she don't have hockey, it is strange that she had the same one yesterday.

I asked the friend about where she got it. She first told me it was from Pick 'n Pay. I then asked if I could phone her mother. She then said now she got it from her father. (They are divorced) I then said could I phone the father. She then changed the story that it comes from her aunt (or lady that is married to the father). I had to leave it at that...

I went and bought another mouth guard as it is already ruined. It is one of those mouth guards you have to heat up and fit exactly to the teeth.

My question is: Do I phone the mother to tell her about a potential issue? It seems the girl is already using the divorce to scapegoat between the two parents. I am sure she told the mother she got it from the father.
Or do I just leave it? (If I am the parent, I would like to know.)