Short answer: Dump her.
Long answer: Of course there are no discounts, its a POS cheap purse that is sold for 1300$ for the recognition value so that people will see and go "wow that is a 1300$ purse!".
The fact she is leeching that off of you rather then buy it with money she worked for is a huge red flag, and she is only a GF now. What happens when you are married? She will bleed you dry.
If she bought it with money she worked for then she wouldn't be an exploiter just looking at you as an ATM to bleed dry and then dump/divorce... but that in turn would still be a sign of serious issues with money management. You cannot have a healthy long term stable relationship with someone like that just as you cannot have such a relationship with a man who has a gambling addiction.
Men who bankrupt their families due to gambling is considered so heinous that any gambling, even done responsibly, is a crime in many countries/states. Pretty nasty double standard that an equally ruinous and mental disorder involving excessive shopping for overpriced trash is socially acceptable.
If you really really love the girl, then stage an intervention because she certainly needs one to not ruin her life and the lives of those she snares.