As per as my knowledge, girls can not join the Indian Air force after class 12th, to join the Indian Air force you need to complete gradation degree to join the Indian Air force.

After the gradation, you are eligible to apply for the following branches of the Indian air force.

Flying Branch
Technical Branch
Ground Duty Branches

Eligibility:

Flying Branch ::

Applicant need to pass bachelor's degree of a recognized Institute with at least 60% aggregate marks.
Applicant age should be between 19 years and 25 years .

Technical Branch ::

Applicant need to pass Aeronautical Engineering in Mechanical Engineering OR Electronics Engineering of a recognized Institute with at least 60% aggregate marks .
Age should be between 18 years and 28 years .

Ground Duty Branch ::

Ground Duty consists of Administration , Logistics , Accounts , Education
Applicant need to have bachelor's degree OR post graduate degree of a recognized Institute with at least 60% aggregate marks .
Age should be between 20 years and 27 years .

Selection procedure:

Written Test
Interview
Medical Test

The written test contains:

Quantitative Aptitude
Reasoning
GK
English