any army related exam after 12th for girls??

No there is no such exam . You can only try only after your graduation is complete . The exam name is combined defence service. It occurs twice in a year. There is no reservation. There is also no  examination fee for a girl candidate. The exam occurs twice in a year in Feb and in Nov. You can appear in both when you are in your third year of your graduation.  It has three stages: one written MCQ, then physical check up followed by interview. Then the candidate goes for a 11 months training period. After which he or she starts working for indian army, navy or air force. Since you are a girl you will get chance mainly in ota which has a retirement after 10 to 14 years if service. And if you had science and maths in 12 and did bsc or btech you can also look forward to air force.

I hope this helps : )