Slink Trev's mate Claire says:

You need to speak to your friend. It's better coming from you than someone who is going to be horrible about it.

I don't know about you, but I would hate to be 'that girl with BO problems' that everyone is making fun of. So however hard it is to speak to her, you've got to help her.

Choose a moment when you're alone and both comfortable. Try and tell her in a way that will hurt her feelings the least.

If it was me, I would gently tell her that the deodorant she uses isn't doing her any favours, and that she should get a better one. And then if she questions why you said that, be truthful.

Tell her that you've heard some people commenting on her body odour, which is horrible of them, but as her best mate you wanted to let her know because you care about her.

Tell her it's worth doing something about it now before the comments escalate and turn nastier.

Good luck!

Claire x