My wife is an amazing DM, and now I'm DMing for the first time ever for a one-on-one campaign for her. HELP!

Ok, I've technically DMed a very few times before in a different system, but I wasn't particularly amazing and I've never done something this small and she's amazing at DMing and I really want to do well so she has a great time!

So what I've got so far: this campaign is set on the MTG plane of Innistrad (pre-Emrakul, post-Helvault destruction for those of you familiar, basically Gothic Horror Trope World for those not). She's playing a GOO Tomelock that's an ardent seeker of knowledge, insatiably curious, and a bit... Well, she described her character as "Luna Lovegood meets Wednesday Adams, who can put on a Jester Lavoure facade to manipulate people", which, I mean how incredible is that? The Patron is the spirit of an ancient, dead dragon whose skeleton rests in a swamp near her home, who I'm loosely thinking used to be a ruler over the continent, or possibly a religious icon who was killed to make room for Avacyn. Input on this would be great. It wants to return to life, restore its power, and use her as a tool to enact that. It's not malevolent as such, but it's been feeding her curiosity and dissatisfaction with her humble upbringing most of her life. They have a sort of powerful teacher, eager student relationship. The opening section is going to be basically her making the pact, and being given both her power and, as such, the ability to make her own way to somewhere where she can pursue her knowledge seeking and the patron's goals.

Context: I've watched a lot of Matt Coville and Crit Roll, including the relevant episodes on 1-on1 play. We're playing in 5e, though both of our experience is extensively and exclusively in 4e (which we both love, but I think 5e will be easier for me to run). We'll be starting her at level 3 (or at lest, she'll build her character at level 3 and get all her class features by the end of the opening sequence, which is where she'll literally make her pact and get the Tome).

Questions: I want her to have a sidekick, a DMPC to both give me someone to lightly steer with, and also just someone for her character to play off, and cover her mechanical weaknesses. Probably a melee Cleric or a Paladin, someone who can heal and be a bulwark in fights. Having some trouble nailing down a particular character, though, so I want some input from outside people. Here's some ideas I'm having trouble deciding between, but I'll happily listen to other suggestions!

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1. Changeling, probably playing with an interpteration playing off, like, Split. Basically mimicing someone is in some ways also sort of giving up some control over who you are. Interesting concept, but I'm worried it would pull too much focus from her character.
2. Wolfir. Former werewolf, curse broken, but now stuck in a (mostly) werewolf form. Due to lore, they're a relatively recent thing in the world, still widely mistrusted, but generally do work for the church protecting humanity against monsters. LOVE this idea, and fits a Paladin really well, but would make it very hard for her to go anywhere unnoticed without going truly solo (not a dealbreaker, but definitely something I'd have to design around), and I'd need to probably refluff a race to represent it. Probably Gnoll (they're in Volo's, right?), or maybe a Shifter or Tabaxi, haven't figured that out yet.
3. Actual werewolf. Classic werewolf tropes to play with, can just use Shifter to represent them, but a little... Predictable? Tropeish? And negotiating full moon transformations once again has a chance to pull focus from her.

Question 2: Holy crap, what do I run? Modules and adventures are all well and good, but I can't just rip out 90% of the mobs, make them solo fights balanced for 1 player and a sidekick, and play normally. There'll probably be a big focus on more non-typical mission types (social encounters, heists, more trap-and-puzzle based dungeons), but I don't know where to begin building those. Are there any resources for this stuff?

Question 3: How should I handle magic items? Is there anything that would be particular useful in a campaign with one player? And how often should I have them crop up, since she largely will be keeping them herself or selling them?

Any help would be greatly appreciated!