You are at right place to find right information. I was in same situation last year extending my fiance mom visa extension. Tell you what, from my last year experience it is very easy to get extension for first time 6 month extension and this should be very good news for you. 

In my case, I filled up all applications and filled on my own. It takes around $240 application fees and you can find B1/B2 visa extension application form in USCIS.GOV website. You would need supporting documents like your bank statement, last year income tax docs, returning itenary to nepal (no ticket needed), recent paystuff  and a letter to consular explaining the reason for extension (any valid and sensable reason is good enough). if you need more convicing reason and info do google there are lots of forum and sites that will provide you comforting answers.

GOOD LUCK!!!!

 Thanks visit2nepal