Frankly, she probably already knows at least somewhat how you feel.
99 times out of 100, when these kinds of conversations happen some form of "I felt the same way, I just didn't want to tell you" gets brought up.
Best to just sit her down and tell her how you feel. Hold the "we want you to join our marriage" idea until you get an answer on how she feels. If she feels the same way, then see if she wants in. If she doesn't feel the same way, better to leave the invitation out.