Wanted to thank you all from the bottom of my heart for your wonderful replies; they mean more to me than I can say! We finally have the little girl in our care... the rescue agreed to release her to us unspayed if we bring her back for a spay once she's reached 2 lbs.
They did a blood test on her before releasing her to us and found that she has signs of a liver shunt already, even at her young age. Looks like we'll have to have her on a special diet and pray that she still has a good life.
We may consider surgery down the line when she's a bit older and tiny bit bigger in size. In the meantime, we'll do our best to help her little body develop best it can. Thank you again for your feedback.