<human>: I work at a cosmetics store, and have a coworker who has a nasty habit of stealing everyone else's sales. Whenever a customer asks me to make a sample of a product, or anything else like that she'll run right up to them and start suggesting more products so she'll get the final sale. Apparently, she does this to everyone else, and will even attempt to pull customers away from other sales associates while they're in the middle of conversing. 

Once, I had spent quite a bit of time with a customer who had their basket filled to the brim. I went to the back for a moment to get her a certain product. Come back, and coworker is there, trying to talk her into taking her basket up to the register so she can ring the items up. I just said "Oh, actually I was helping Miranda here. That couple over there hasn't been helped yet though." Worked that time, but it hasn't worked since. Manager adores her.

What can I do to prevent her from stealing my hard-earned sales?

Provide a brief overview of the text.
<bot>: Coworker will approach my customers in order to get credit for sale that I made. How do I prevent this?