I'm going to ask my gf of 3 years to consider using her inheritance to buy a property
Why should your gf buy the property and not you?
It's a good idea, I don't want her to waste money on other stupid things
While it is not technically your money, it is nice that you are giving her sound advise about investment opportunities. Real estate is a great thing to invest in since you can make money off of it. If your gf agreed, then she could be on her way to having her own home.
Yeah, but mostly I'll have a free place to live, which is what I really want.
Even if your girlfriend buys a house, why should you get to live there for free? You should probably offer to pay rent if the relationship is important to you. Otherwise, she might dump you for a more successful guy.