At the root of the issue is whether or not you believe that your boyfriend is the kind of person who can deal with someone like this woman in a way that would protect the relationship he has with you.
What she did might be inappropriate. That is a somewhat subjective determination. I think it's inappropriate because of the cost of the gift. It seems excessive. She apparently harbors much affection for him. She might be manipulative or she might be deceiving herself into thinking that they are "just friends."
Do you think your boyfriend is able to understand that, and be willing to draw a line?
I agree that contacting her was not a wise move, although I understand the emotions involved. You are protecting your turf. But since you don't have a relationship with this woman, you only risked alienating your boyfriend, because she doesn't know you and therefore doesn't care what you think.
if you demand he do something, you are attempting to exercise control over the situation. It would be much better if he were the one to set the limits and deal with her appropriately.
Some men will be pigs and will deliberately try to woo other women. Most men are simply ignorant of what is going on, and get sucked into a situation in which they can do stupid things.
Talk to your boyfriend calmly about the situation. Express your concerns and fears. Emphasize that you trust him, and that you know that he would discuss things with you if he ever began to develop feelings for this woman.
Good luck, I wish you the best.