When did the house-buying BS start? Has that always been part of the equation because today is the first I've heard of it.
Well, I think if she somehow doesn't know you really like her, she's an idiot. Meaning, she's GOT to know you like her. So, why would an INFJ stay in a relationship like that? It's possible she's trying to salvage/improve the relationship through building a home with 7yr-loser. INFJs always are thinking of the future and fantasizing about 'what could be', often to our loss.
Like Jeno said, your INFJ is in complete control of the situation - she' not going to do anything she doesn't want to do. I think that once she buys that house with the dude, there's going to be a CONSIDERABLE sunk cost in that relationship (not to mention the previous 7 years), making it even more difficult to leave the relationship in the future, at which point I think you won't have much of a chance.
If you're going to do something about this and have no regrets either way, I'd say it's time to man up and tell her clearly and plainly to go with you and leave the guy. Frankly, I'm surprised she hasn't already left him if she's serious about a possibility with you. Furthermore, the whole house thing raises the hair on the back of my neck as to how healthy of an INFJ she is (if she truly is unsatisfied in the relationship).
If you're going to rescue her out of a situation she's choosing to stay in, coaxing with softing wooing may not work anymore. Sometimes a damsel in distress needs to be swung over the shoulder of the knight and carried away.
That's my 2 cents.