Speaking as someone who DMs a campaign with one PC, you don't need specifically designed adventures. Just use adventures about 4 levels below your wife's PC's level to account for the party's lower level and action economy poverty. I also added ongoing NPCs which she could travel with, RP off of, and take on adventures or not. Leadership is a must-have feat. The cast includes: a BFF, a brother, a pseudodragon, a medic, some Paizo goblins she's converting, and several non-traveling NPCs. You want a stable of characters for some simple reasons. She'll need someone to RP with and that's easier with ongoing characters. She'll need someone to bounce strategic and tactical ideas off of, because it's damn hard to do that with no help. It provides some combat cushion to prevent early-death syndrome.
Three keys to making this entourage a success:
1. The PC is the star. Do not treat the NPCs like they are your characters. They're tools to make the experience fun for her. She makes decisions, they provide advice and support. I flat out ask her what she wants her friends to do in combat situations; it's only if she doesn't have an opinion do I use my own judgment.
2. Do not make the NPCs finicky to play. You have tons on your hands running the world and running these NPCs is an extra thing for you to handle. From 3E, the classes should be fighter, barbarian, sorcerer, dragon shaman, favored soul. A wizard with an encyclopedia for a spell book or a shape-shifting summoning druid is a stupid move on your part.
Corollary: Do not make the NPCs powerful. She is the star, they are the entourage. Give them under the hood feats that boost their saves or add pluses to their attacks. Do not give them additional options and don't stress about making them well-designed. Being underpowered is part of their job description. No metamagic cheese, no awesome feat synergies, and they get the leftover magic items at the PC's discretion.
3. Each NPC starts with one note personalities. In my campaign, the brother gives the jock perspective on things, the pseudodragon gives the scheming side of things, the BFF gives the geek kid sister view, the medic gives the stick-in-the-mud view, and the goblins give the rampaging id view. It keeps it simple for you and keeps it clear for her. Complexity comes in year two.
I own a couple of their other (non-adventure) products, and I'm glad I do, but that's probably not particularly relevant here. I can, with total honesty, say that I'm not - even remotely! - connected to the company or anyone who is or ever has been a part of it, if that helps. 
