My weights

Ok so im 169cm tall which is 5'6
Before this all began i weighed 57kgs... (125lbs) my BMI was in the normal range...
June 2007 I weighed 52 kgs... still ok.
May 2008 I weighed 42 kgs, (92lbs, 6.6stone) this was the lowest i had ever been, it put my BMI at 14.5... underweight...
August 2o08 i got back up to 50kgs... apparantley still too light... :(
October 2008.. today im 48kgs... 105lbs..

I know i shouldn't say this but i i really want to be back under that 100lb mark... so 44kgs...
I know i should not be controlled by a number.. but its how i feel...

My sister wants me to be at 52 or 54kgs but i jus dont think i can stay at that weight and be happy about it. I think if i get under 100lbs i will be happy but deep down i know i wont be. I wasnt happy before. But who knows, I can only try. right?

thing is as much as i want to be under 100lbs my sister is trying to help me recover... and she always makes me feel bad if i dont eat and said that if i get to that weight she will be VERY disappointed in me.. so i dont know what to do.

Do i ignore her and do it anyway or do i listen to her and try to recover.. i know what the RIGHT thing to do is, but i juust dont know if i can!