Ask her to do what she wants to do.If she is interested in btech ask her to do if she has science in 11_12. If she wants to take bsc in any subject ask her to do or if she studies arts ask her to do B.A.. Don't pressurise her. Let her do what she wants herself.let her listen to the voice of her heart.

Thank You 

Hey,
There are plenty of fields that are worth giving a shot to depending upon the interest of the individual.
If your sister is from  Science stream then she can go for Engineering(Provided she has Mathematics in 12th). She can go for Bachelor of Science in various courses like Physics,Chemistry,Biology,Biochemistry,Microbiology,Biotechnology etcetera.
If she is from Commerce background,then she can go for Bachelor of Commerce. If she is from Humanities then she can go for Bachelors of Arts in various courses like English,History,Political Science etcetera.
She may even go for BBA or BCA and later go for KBA or MCA respectively.
She may even go for Law for which she can appear for CLAT.
Hope this helps.
Good luck.