I am female OCI whose completed education of 12th in India, Will I be able to avail the open category female supernumary seats in IIT?

Yes you can avail the supernumerary seats in IITs. OCI students are treated as Indian Nationals if they complete 12th class from India. But if someone tries to study in India after completing 12th or equivalent from other countries, he or she will be treated as Foreign Student.

Female supernumerary seats were created in 2018 to increase the female students in engineering colleges and to provide extra opportunity to female candidates. Previously the male female ratio in engineering colleges were 10:1 and after this decision the ratio became 7:1.

All the best.