I Rescued 2 3or4 Week Old Sibling Kittens . The Female Kitten(Callie) Walks Really Low To The Ground And On The Top Of Her Toes Sometimes Like She Forgets To Lift Her Feet All The Way. Is This Ok?

Callie and Mr bigs are brother and sister. Mr bigs walks perfectly fine, Calli however walks crouched to the floor and sometimes on the top of her toes, she fell off the porch rail and i wonder if when she landed on the trash bag if she hurt her left side. Before this she had a serious attitude and was hissing all the time but now she only meows quietly.