I'm going to request my roommate that her daughter use the downstairs bathroom
Why do you want her to use the downstairs bathroom?
The upstairs one is for showering only.
Well, it's your home, too, and you are entitled to personal space inside it. Hopefully the daughter will comply.
Yes! I won't ever have to see her in my downstairs bathroom anymore.
You should feel comfortable in your own home. Even if you don't like the friend don't you think you could be nice to them maybe they don't have parent who care or something.