Go to the local wada karyala with a copy of citizenship of you both, two copies of photo of you both and photos of your marriage and ask them for a marriage certificate . These days they give a marriage certificate written in both nepali and english. That will work.

Besides that you will need following documents.

1.Birth certificate of both
2.Joint property or joint bank account
3.Notorized affidavit letters from your relatives stating that the marriage is a bonafide one
4.All visa pages of passport of you both
5.Marriage photos , travel receipts, flight receipts of you together
6. If possible take job experience letter and police report of your spouse, letter of intent from your spouse stating that she will immigrate to usa once her petition is approved

That should be enough to start i130 for your spouse