The girl next door has body odor, how should I remind her so as not to hurt her?

When faced with a person's shortcomings or physical defects (such as body odor), we should usually maintain an understanding and tolerant attitude, rather than dislike or even blame!

The girl next door has body odor. I suggest you find a suitable opportunity to talk to her alone and tell her how to deal with body odor, such as: eat more watermelon in summer and drink more water in winter. Eat less barbecued, fried, salty, sweet, spicy, fishy, ??meaty foods, etc.

The most important thing is that after you tell her the situation, no matter how she faces you, treat her the same as before, or even care about her more than before. Even if you may hurt her when you tell her, your actions afterwards will make her feel that you are not laughing at her joke or even mocking her, but you are helping her.