There are various ways.
How would a non-Nepali speaking person find her way through the villages of Nepal?
Re your mother, explain to her a few things that she will need to know during travel: flight environment, US entry, transit, etc.
She should have her travel info, US address and Nepal contact details HANDY, and ALL in English.
If she is transiting/connecting flights, instruct her to show her travel itnry to anyone in uniform NOT carrying a broom or bucket. Usually those wearing a 'blue' or 'smart uniform' with a name tag on their chest are airline/airport workers. Your mother does not have to be able to read their names.
Instruct her to just show the travel paper/s at any airline counter/window.
She has to get her time correct. You might as well have her set her watch to the time at transit city before she leaves Nepal.
Make her understand that not all travellers speak english, and that she is not alone.
Maybe have her carry a translation card: PAANI - water, etc.
Usually there are hundreds of other Nepalis in flight from Nepal. Maybe she can be hooked up with some right kind of person to help her at transit, and during flight. Also, it is very rare to not have another Nepali going to USA on same flight these days.
Have you phoned/emailed the carrier? Usually they can take care of these issues much better than you would imagine. Let them know that she is old, does not speak english, and needs assistance.
BTW, us nepalis have a very Nepali habit of carrying too many poka puntura... and this causes problems in travel for your mother. Tell her not to carry any poka puntura in her handbag, stuff them all in the checked-in suitcase and she won't have to worry about it until she reaches USA. Also, it is wise not to bring those gundruk and bandel ko achar, etc that could create difficulty for her.
Hope this helps.
_x
