Nepali Alphabet:
You should give enough time to the basic things than taking him/her to the complex words. I think 2-3 hours tutoring + 2-3 hours self-practice will be enough.
1. Write consonants "Ka" "Kha" .... "Gyan" and teach him/her how to pronounce it. Tell him/her how each syllabus has a vowel attached to it. Then,
2. Write "A" "AA".... and teach her how to make vowel sounds
3. Now combine those consonants and vowels in very simple words, e.g. Kaka, Mama, Aama, Baba, Dada, Didi, Babu etc. I suggest you to start with relationship words while giving enough time to memorize those words.
Mastering steps 2-3 is very important because he/she will have to write the Nepali words in the roman style as you teach him/her at next levels.
Then you can go ahead with
Nouns: very common words like Bhat, Dal, Alu, Ghar, etc. etc.
Pronoun: timi, tapain, tan, ma, mero, timro, afno, etc.
Verbs: Don't worry about correct tense and subject verb matching. Maile khayo = maile khayen... everybody will excuse a khaire when he says maile khayo.
however - differentiate the meaning of khanchhu and khayo (tense wise).
Practice 10-15 common verbs.
Preposition: ma, tala, mathi, agadi, pachhadi, muntira, mastira (they will find muntira/mastira funny and learn and remember those words easily)
Adjectives: Color - rato, seto, khairo, kalo, nilo, hariyo ... don't feed to much with 35 colors that you use to describe the color of lipsticks; measurement - sano, thulo, barabar, lamo, chhoto, utrai (let him/her say "ma dherai lamo chhu" for few days and correct later).
hahahaha...... do you need more help? Pay me $$$ /hr :-)