today mom ask me to take my 16 yr old sister to the mall

i got mad because my mom let my sister go everywhere she wants with her friends , dates , boyfriend etc since she was 15 by herself and now she is like take your sister to the mall i say i only can take her at 11 she was like is too early   and she doesnt understand that i cant because i have a daughter in school and i have to go with her to eat lunch at 12 ... we dont live in the same house but is the same problem every single time that she wants to go somewhere and my moms excuse is i dont drive too far because of my glasses but my question is why you let her go if you cant take her? and why when i was almost 18 you didnt let me go nowhere ? im 25 by the way