Hi @pagesbypatti, let's jump right into this!
When you say that she shared her Dropbox I'm guessing you're referring to a shared folder, right? Or is she sharing her credentials with you?
If you're talking about a shared folder, that is expected because the files exist in your account.
When you have access to a shared folder, you're not accessing someone else's folder. You're accessing your own copy of the folder within your account, and you need to have enough space available to hold that folder.
I hope this helps!