I am 5 foot and half an inch also! My doctor told me to aim for 7 stone 7! But I think this is a little low so I am aiming for 8 stone. Before I went to University I was 8 and a half stone and a size 10 so I am thinking that 8 stone will be a nice size 8-10 which on someone of my height (tiny) looks healthy I think.
Hope this helps!
I can't imagine being 105 pounds. It's so far off. I guess it's possible, but I can't remember ever being that weight.