satchboogie, your question is impossible to answer. First, without some extremely sophisticated equipment, it is not possible to measure how much of your gain in fat-free mass is due to nett nitrogen deposition (in other words true muscle growth), increased hydration of existing muscle, or increases in bone density. On top of that, everyone is different. Thirdly, the law of diminishing returns apples as WarLobo pointed out. Fourthly, it depends on where you're starting from. In my case, I started at 5'5" and ~105 lbs. There was nowhere but UP for me to go in terms of muscle gains. At 160+ lbs, there is little chance I can gain much more muscle naturally.
So maybe a woman could put on 15lbs LBM in her first year of training, 5-10 in her next year, 2-4 in her third year, and only a pound or two after that (if she's not too old like me). I would think that would be pretty good going for your average natty female!! I also want to point out that MOST of my keepable LBM gains have occurred post-competition dieting. There is no way I could have gained as much as I have without that rebound muscle growth that comes from dieting down to very low bodyfat levels. Most importantly, that rebound muscle growth also requires some rebound fat growth, and if you are unwilling to put on some fat, then your chances of contined growth are not too good without AAS. I'm not talking about slobbing out and eating all the junk food in sight....just good quality muscle and moderate fat gain.