How to tell my mom that she smells bad?? :/?

So here's the thing, my mom stinks. She takes a shower every other day, but only washes her hair once a week (because the way she does her hair takes hours, and she doesn't have time to do that every day). Her hair/head is what's giving off the stench. &since she's short, basically everyone towers her, and I'm sure they can smell it too. With the summer, the sun shines on her head, and makes it worse. She's really sensitive, and insecure. How do I tell her that she smells?