No, if you feed properly, she won't go from her current size to 7'+ in only 3 years. Most of the boas you see online reaching 7' before, say, 5-6 years, are usually power fed. This is unhealthy for them, and cuts their life short. Most likely, you're looking at 6+ years old to see 7', if she ever gets there.
No interest in over feeding to make her grow large, She can be whatever size she gets to. I just want to be prepared for how big she might get.