THIS IS A GREAT QUESTION!!! I commend you. I see a lot of silly questions, and it is nice to see a good one.
You can interview another agent and get a free CMA. But, if you do that you always run the risk of another agent trying to "buy" your listing by giving you the false impression they can sell your property for more than the last agent told you.
If you are pretty sure that you will use the one agent you have a relationship with, that is a great loyalty.... you can your preferred agent to hold a brokers open BEFORE the listing goes public and get feedback on the price from other agents-in her office or others. Or, you can just ask her if there is another agent in her office that would give her a second opinion before it's listed.
I would just explain to her that you know pricing in this market is key, and difficult even for the best, most experienced agent, since the market is fluid... and you are highly motivated and want to sell quickly without leaving any money on the table. I think she'd respect that a great deal. I know I would.
Or, you can ask any agent to provide a CMA for a fee - completely negotiable. It;s totally your call... whatever makes you feel more comfortable.