Like July said, I've got a few questions relating to YW-verse.
First, if Lisa's a wizard-in-training, has she gone through her Ordeal yet? I guess I'd be lying if I said the prospect of that coming up in the course of a future mission didn't intrigue me. One of the things I really like about YW is that the PTBs can plausibly turn up anywhere, including other canons (though, in LotR, for instance, given that Morgoth is trapped in the Void, it's probably safe from any personal appearances by the Lone One). On the other hand, given that a wizard's Ordeal can a big freaking deal, occasionally world-changing, I'm a little leery, too. Do you have ideas about handling that, or has Lisa already gone through it? If she has gone through it, what happened? That's an important thing to know for a wizard character. Also, what does the Lone One look like to her? As I recall, It's supposed to look different to everyone (though I think even Diane Duane forgets this for convenience).
Second, new wizards have a lot more power at their disposal than more seasoned ones. I can tell you're making sure to limit how much she can do, so I'm not too concerned about that—actually the opposite. The nature of YW-verse is such that I'd really expect its magic to work anywhere, though of course the wizard would have to become intimately acquainted with a given world's name in the Speech in order to be effective at casting in it. I think the mechanics of YW-verse magic are limiting enough themselves, as long as they're borne firmly in mind and respected. I'd hate to see it nerfed beyond that.
Third, I am a little concerned about Lisa herself, based on the RP. While the fire was going on, Lisa tried putting it out and failed, and then this happened: "Lisa swore and went to go off and collapse on a couch. Maybe eat a cookie. She didn't really want to deal with other people's problems right now. Particularly when she was so new to magic."
Wizards are supposed to be combating entropy—Lisa agreed to it when she took the Wizard's Oath—and an indoor fire that could end up with people getting hurt or even killed seems to fall solidly into that category. "Dealing with other people's problems" is part of the contract, so her willingness to leave everyone to their fate really worries me, new to magic or not. As I recall, that sort of attitude can get a wizard stripped of the ability to use magic, and probably any memory of having been able to do so.
I see two options here: One, you're running with this characterization. If that's the case, I will expect a reckoning for her carelessness with the power she's been granted. If she doesn't take her Oath seriously, she's in big trouble.
Two, that was a fluke, and I will expect her to behave like a wizard.
On more of a side-note, I sort of assume her work in the PPC would be official errantry, since badfic is definitely a force for entropy (and one even the Lone Power may not like much, at that), but that doesn't mean other commissions can't come up. Since conflicts between one job and another could be really interesting, I'm curious if you've thought about it.
I think that's everything I wanted to say. I also second July's specific comments about the writing sample, though I'll note that solo missions do happen, if not generally to very new recruits. Still, they aren't encouraged or the norm, for the reasons July gave.
~Neshomeh, also holding off on a yea or nay for the time being.