How do i nicely tell someone they smell?

Short story, there's a kid in my class who smells like "cornstarch mixed with piss" I know the girl well enough that she doesn't have the greatest home life so I don't wanna be overly blunt like I normally am when talking to people.

I have tried mentioning it once when I was sitting next to her by saying "something smells like cornstarch, can you smell that?" But that didn't work.

She comes to school every day like this, I feel like I'm not good enough friends with her to tell her though.

What is the nicest way I can word the she needs to shower?