She expected me to purchase her items with the gifted money.
It looks like you're the one dating a materialistic girlfriend and not you friend. So you should man up and stop saying my friend's girlfriend.
Ladies want to be loved, cared for and pampered with gifts, especially on an important day like the Valentine's day. However, just as all shoes have different sizes, that's how we all have different financial capacities. If a lady cannot accept or is not satisfied with the gifts and money I can shower her at my level. Then, It's a red flag for me and I'd gladly pack my bag and baggages and run a way, because I'll not steal to impress a lady.
You noticed that too. I thought I was the only one who noticed. I also think that the OP's girlfriend is what he is referring to; he is just pretending to be girlfrined by other people, but this is just my guess. Valentine's Day has become a tradition in other countries, including our country.
For two partners, if they truly love each other, whether there is something to give or not, but they wish Happy Valentines to each other, I don't think there will be any problem with that. But if one of them gets angry or hurt, I think that one of them has not really understood the true meaning of a relationship.