Years go by. You and your friend stay in touch, compare querying experiences, talk author stuff. Finally, she lands the agent of both of your dreams. Her book gets published. You're happy for her, and thrilled you were a part of her writing process - even if it was waaay back when.
You, too, have queried Perfect Agent. She requests your manuscript - the whole manu - and she reads it. She gives you some suggs and passes on it.
You come to find out your friend's story is not the same story you helped her crit way back when. In fact, it's about the same thing your story is about.
The question then becomes: did Perfect Agent request your manuscript just to see what you were submitting to other agents because she'd just bought and sold a story ( your friend's ) very similar??
How would you feel? What would you think?