If you and your husband are both students, you probably will have hard time proving that you will be able to financially support your mother in the US for 6 months. There are two ways: you pay for her trip or your mother pays for it. If she can make papers (bank papers, property valuation etc) from Nepal, she can say that she will pay for her own trip. This way, she will have a better chance of getting the visa. Good Luck !! D