Too many treats!!

My friend constantly gives her pony treats, and it is really fat! If that were my horse, I'd probably never give it treats.
I'm not even kidding, if you went to score this pony's body condition, it'd probably be an 10 out of 10 all over!!... And it's already been foundered a couple years ago!!
If you think I'm being mean, get this: she leaves a bag of treats for him to eat while she's tacking him up, and he like takes mouthfuls! And her girth is the same size that I use for my pony who's at least 3 hands taller.
The pony's not mistreated in any way (besides the excessive treat-eating), he's just really really spoiled.
What should I do? Should I tell her not to feed it so many treats? I just don't want to sound bossy since she's not a whole lot younger than me.
Advice please.

Other than gently advising her that she might want to stop giving her pony treats, there's nothing you can do. I'm sure she knows she's over feeding him.

Ya I would let her know that this is not good for her ponys health, maybe do some researching about what it can do and let her know its not good.

If her pony foundering wasn't enough to open her eyes, there's probably nothing you can do to change her attitude

Maybe having a respected adult (trainer, vet, etc.) talk to her parents about the danger it poses to the pony's health might keep them from buying the treats for her?