Are my feelings for this girl moral??

I believe that I have fallen for my former foster sister. For those who don’t know what a foster sibling is: a foster sibling is the biological offspring of an adult that is taking care of you through a government agency while your biological parent cannot take care of you. I am friends with members of her family. My mother is best friends with her mother. She might be two years older than me but I like her a lot for some reason. I am not blood related to her and we do not live under the same roof. Help! Are my feelings moral??