Hello,
You must see that you end up the relationship cordially. Since she belongs to north east police/ administration will have soft corner for any complaint lodged by her.
Talk to her and to her sister that such is the thing (whatever if the reason) and therefore lets part ways mutually.
If however, she does not agrees for the same and files and FIR after you leave her then the only option we will have to is fight the case on the ground that the complaint has been filed for wreaking vengeance.
I hope you understand that you can not stop anyone from filing a complaint against you and Indian laws are in favor of the girl therefore you are advised to act wisely at this juncture.
Let me know if I can be of some help.
Regards