Can a mom apply for unmarried daughter's green card

[needhelpnow]

On the USCIS site it says that a permanent resident can sponsor an unmarried daughter/son regardless of age. I was wondering how long the process will take if my mom who has a green card can applies for my sister who is 30 but unmarried. I know that family based green card takes around 13-14 yrs(my mom got hers since my uncle sponsored her and it took 13 yrs for her). But is it going to be the case with my sister also since she is dependent on my mother. And what kind of form needs to be filled out for that and what's the waiting period and does she need to do that before coming to US or after she comes to US she can apply for my sister. Please let me know ASAP.

Thanks much in advance!