Pumpkinpatch, you didn't come across as knocking her down, at least to me. When my husband and I were young and bought our first house years ago, I asked the same question of the real estate agent who was representing us. How do you get paid for your work? I thought it was a fair question - if the agent gets paid a percentage of the purchase price, then how is it in her best interest to negotiate a lower price for us? That means a lower commission for her. The agent did some verbal dancing until I reassured her that I had no problem with getting paid for her hard work. I wasn't being mean and nasty, I was simply trying to understand the process.
I would ask the rep how it works in her industry. Simply say what you've said to us. You understand she deserves to get paid for her work, but how does she get paid? Is it commission-based? Salary? Referrals? You feel that she took the time to educate you and you'd like to return the favor by hopefully spending money in her direction. When my husband and I are out shopping for expensive items but want to think about the purchase overnight, we always ask if the sales person who has been helping us is on commission. If they are, we make sure we get his/her business card, especially if they've been very pleasant and helpful. That way if we decide to make the purchase, they will get the commission.