I played this game on PS2 and I really enjoyed it. I played part of it on 3DS and thought it was a great port. The difficulty is not too bad, and the good thing about RPGs is that there is always grinding if you do hit a difficult part. I would recommend this or Fire Emblem if she is an RPG fan. Fire Emblem is more SRPG, but it is one of the best games on the console.
Goodness, to answer easiest, it is all relative regarding what you are referring to as easy. If you are talking about basics of entry, I would say Pokemon X or Y because the battle system and linearity help keep the game simple (I played out of nostalgia, but got bored to tears - Just finished before paying Pokemon an in depth RPG with similar elements in Shin Megami Tensei IV).
Some games to consider are:
Etrian Odyssey IV - has some lower difficulty settings, but turned out to still be a great game even on the lowest setting (complicated only if wanting to build a specific team). Played all the way through and had a decent storyline with great dungeon crawling exploration. Think Wizardry, but easier point of entry.
Fire Emblem - Wonderful storyline, has lower difficulty setting, EPIC. One of the best games on the 3DS
Shin Megami Tensei IV - Great game, not too difficult, lengthy, but a little iffy on how they view religion, God, and demons. If that would bug you, I would steer clear.
I wish you luck. There is a great number of great games, including RPGs on the 3DS. I would check Metacritic and look for "Role Playing Games" if you wanted to read some other user reviews besides what is on Amazon.com.
I gave all those games consideration. She gets bored with Pokemon fairly quickly. Bravely Default looks like it may be what we are looking for. It looks easy enough yet interesting in story. I am playing Etrian Odyessy Untold Story, Fire Emblem, Shin Megami Tensei IV, she might like the new Pokemon.