C.T.
Hi K. - I think the best way to deal with this is to not make a big deal out of it. I dont think anything needs to be said at this point. This doesnt mean that you are being dishonest, you are just allowing the friendships to develop naturally.
The two of you can have a great friendship even without your kids being best friends. Just the circumstances of your daughters activities with other friends will naturally limit their friendship. Encourage your daughter that when this other girl comes to play that she should always be friendly and reassure her that it doesnt mean that they are expected to be best friends. Rudeness is never an option.
It's an important lesson for our kids to learn that we can have lots of different kinds of friends and different levels of friendships. On a practical note, it might help your daughter to have some ideas prepared of things they could do when they are together. This really helps when kids have differing interests from one another.