What is this Freedom Tennis of which you speak?
That sort of thing is always awkward. I have had the duty of playing with people who wanted to join teams I captain, and it is no fun at all when they don't measure up.
Are you sure she wouldn't make a good doubles partner? How were her overhead and her volleys? I ask because I do very well in doubles but am a USTA level lower when it comes to playing singles. So if you were looking for doubles maybe she would have been OK?
Maybe the ideal tryout next time would be to find two other doubles players and then you and this lady could have played them. Then you could have evaluated other important doubles skills -- especially attitude and positioning.