Hi! Thanks for the question!
The case falls under Section 5, Citizenship Act of 1955.
After the marriage, the girl will have to wait for seven years before she can apply for Indian Citizenship & apply for Indian passport on basis of this acquired Indian citizenship. The best course the Government of India provided for all such cases where Indian citizen marries a foreign national is to provide such foreigner spouse PERSON OF INDIAN ORIGIN CARD (PIO CARD) by virtue of all such benefits accrue to such person:-
1)No visa required for visiting India.
2) No separate “Student Visa” or “Employment Visa” required for admissions in Colleges/Institutions or for taking up employment respectively.
3) A PIO Card holder will be exempt from the requirement of registration if his stay on any single visit in India does not exceed 180 days.
4) In the event of continuous stay in India of the PIO Card holder exceeding 180 days, he/she shall have to get himself/herself registered within 30 days of the expiry of 180 days with the concerned Foreigners Regional Registration Officer / Foreigners Registration Officer
5) Parity with non-resident Indians in respect of facilities available to the latter in the economic, financial and educational field.
6)All PIOs including PIO Card holders shall enjoy parity with NRIs in respect of all facilities in the matter of acquisition, holding, transfer and disposal of immovable properties in India except in matters relating to the acquisition of agricultural/plantation properties. No parity shall be allowed in the sphere of political rights.
7)Facilities available to children of NRIs for getting admission to educational institutions in India including medical colleges, engineering colleges, Institute of Technology, Institute of Management, etc. under the general categories.
8) Facilities available under the various housing scheme of LIC, State Government, and other Government Agencies.
9) Special counters at the immigration check posts for speedy clearance.
The marriage should be registered under the Special Marriage Act.