What a little darling Carrie! The first thing that comes to mind when you mentioned her size, and neurological goings on, is a liver shunt. This is when the blood vessels going into and out of the liver are malformed and not filtering things as they should be. It can cause a cat or dog to be very undersized. I had a very tiny kitten some years back that my husband dubbed "Molecule" (Molly for short) and she was no doubt a liver shunt baby according to the vets take on things. Surgery is high risk, and very expensive too. Dear Molecule survived till about 8 months old, but looked about the size of a 6 week old. Here's a link to liver shunts... http://www.vin.com/vin_ce/abvp/html/liver_shunt.html
You may want to mention this to the vet along with possible heart problems as mentioned by kb2yjx. Heart defects however are pretty easy to diagnose, whereas liver shunts require MRIs etc. to properly diagnose. Her bent legs could be radial hypoplasia in which the bones in the forearm are bent to varying degrees. My Kirby(the handsome boy below) has the severe form called radial aplasia where there is absence of bones in his front legs. It's a birth defect that occurs once in a while with polydactyl cats, although Kirby is not a poly! Keep us posted on that little cutie. Another great place to search (and bookmark) is www.messybeast.com Give her a whole mess of kisses for me please! Jan