I don't think you can even begin to estimate an adult weight for her since she has had a rocky start. She could be very behind her normal growth pattern and catch up after a few more weeks. She may always be tiny though. Just too soon to tell when she was not fed naturally from the start.
I lost a momma dog and had to hand feed the whole litter. The smallest one would not suck on a bottle. I used a dropper to feed him. He stayed the tiniest for quite a while. I kept trying the bottle here and there. Finally a day came that he took it. Then he started gaining weight better. Once they started on puppy food, he ate like there was no tomorrow!
He actually became the larger of my males before it was time for them to find homes. So, you can never tell. The prediction charts work VERY close for me once the puppy is 8-12 weeks old, but before that too many factors play on their tiny weights, especially in cases like this one.