That is what i-94 is for. US keeps records of arrival and departure
date of each and every individual or assumes it should have record. If
she goes back to nepal and applies for visa later on, they they will
see that they have arrival record but no departure record of her; this
makes the thing messy, unless she has a very good reason for that, she
may get denial for visa.

Now u may say you don't need to give i94 if u travel by land, well u don't need if u r returning back within 30 days. If u r not returning back within 30 days then u shud give ur i94 at border.

 u may want to read following:
arrival departure laws.

It is your responsibility to ensure that your I-94/I-94W is turned in to Customs and Border Protection (CBP) at the end of your visit to the United States.

• If you are departing by air, please turn the I-94/I-94W into the airline prior to departure.
• If you are departing by sea, please turn the I-94/I-94W into the shipping line prior to departure.
• If you are departing by land and you will not be returning to the United States within 30 days, please turn the I-94/I-94W into the Canadian or Mexican authorities upon departure from the United States.

Be sure to turn in the CBP Form I-94 or I-95 to the proper authorities on departure. This returned portion of the form proves you did not violate U.S. laws by overstaying your period of admission and staying in the country too long. It is evidence that you obeyed U.S. immigration laws and left timely, which is essential if you want to return to the United States at a future date as an immigrant or nonimmigrant.