The way I look at it is this: Sales Reps don't get every piece of business they pursue. They're used to hearing "no" and understand logical reasons as to why they didn't get the bid. If you can tell her why she missed out, she'll understand and respect it...and she'll know better how to approach the next opportunity she will have with your company. She'll also appreciate the feedback.

And I see nothing wrong with letting her know that you enjoyed working with her through the bidding process, and "don't be afraid to give me a call if you find yourself in danger of sitting next to an empty chair in the skybox".