My friend did the same thing....and IIRC, as long as her name is not on the mortgage/deed, it is still yours regardless if she has paid you rent.
On the relationship side of things....yes, it is YOUR condo...but don't act like it when she moves in. If she is going to be paying you rent...and moving her belongings in, you are going to need to be flexible and comfortable.
Yes, you always have to think about "what ifs", but try not to let it affect your relationship.
Also, congrats on taking the next step...this should be a happy time for you two
