Answer:
To understand my explanation you need to know what homosexual is.
A Homosexual is someone attracted to their own gender.
L stands for lesbian. A lesbian is a homosexual woman.
G stands for Gay. A gay person is a homosexual person. (gay is mostly used for men)
B stands for bisexual. Someone bisexual is someone that is attracted to both men and women.
T stands for transgender. People that are transgender don't classify as people of their same gender.
Q can stand for queer or questioning. That is when someone is questioning if they are L, G, B, or T.
Good luck with your sister.