I feel it's a good idea to talk a bit about Luna as a character, to avoid some confusion.

Luna is a character which is a bit complex to describe. No single statement is adequate for a description. I think it's a mistake to take one of her aspects and then stereotype that aspect, and insist the acts like the stereotype. It's a much deeper combination. Yes she's intelligent but that does not make her argue like a scientist necessarily. Yes, she's an idealist, but that does not make her naive or even rigid.

Some may object to me using human personality types to portray pony characters, but let me assure you that I am taking into consideration a full spectrum of traits. So to begin with as a base, let's take a look at the INFP personality, which I think portrays Luna's inner workings rather well. And to show that I'm not relying solely on this, I am only hand-picking the traits which I feel describe her specific character the best.

INFP personalities are true idealists

I think it's arguable that Luna is an idealist. It is idealism that drives someone to insist that others appreciate their work - her initial foray into evil was because she felt under appreciated. Being an idealist is more of a burden than a benefit, oftentimes.

While they may be perceived as calm, reserved, or even shy, INFPs have an inner flame and passion that can truly shine.

I think this quote describes Luna quite well. Extremely well, in fact.

the risk of feeling misunderstood is unfortunately high for the INFP personality type - but when they find like-minded people to spend their time with

I'd agree with this. One of Luna's key motivations is to find someone who she can consider herself a peer to. The most likely candidate would be Nyx. And yes, like Nyx, Luna is often misunderstood.

INFPs are guided by their principles, rather than by logic (Analysts), excitement (Explorers), or practicality (Sentinels). When deciding how to move forward, they will look to honor, beauty, morality and virtue

This is one of those traits which I'd say is prompting much of Luna's more... heated discussions with other characters. If something violates her principles, she is not shy about letting them know. Her pragmatism has limits, but when she is able to put away her idealistic traits, she can be very pragmatic if the situation calls for it. This may be viewed as an inconsistency, but truthfully, none of us are perfectly consistent.

INFPs have a talent for self-expression, revealing their beauty and their secrets through metaphors and fictional characters.

This scene from Snowdrop: "The only one who ever truly knew my night." Understanding precisely why Luna said this is a good step toward understanding her inner thought process.

Unlike their Extraverted cousins though, INFPs will focus their attention on just a few people, a single worthy cause - spread too thinly, they’ll run out of energy, and even become dejected and overwhelmed by all the bad in the world that they can’t fix.

This, I believe, is Luna's #1 struggle during the time period of my story. Couldn't have said it better.

If they are not careful, INFPs can lose themselves in their quest for good and neglect the day-to-day upkeep that life demands.

This fits the situation where she calls Nyx in for a heart to heart talk. She has been so overwhelmed by the new burdens and responsibilities that she has neglected the friendships that were once close.

Luna is also known for being fairly reactive. We see this in her #1 MLP episode Luna Eclipsed. she's passionate, reactive, and confrontational, but also puts effort into keeping her emotions in check externally. Most of her fury and fire are on the inside. But that does not mean it is not there.

So how does this come into play in my story?

Well, I also have Luna being extremely intelligent but that trait is not her dominant characteristic. It is simply there. She can mentally spar with someone like Spell Nexus, without losing her footing.

So what's going on in that dialog she's having with Nexus anyway? Well to answer that, it's important to understand Nexus himself a bit more. In Past Sins, Nexus was thoroughly intimidated by Nyx. Even when she wasn't being intimidating. Nexus has a fear/respect relationship with those in power. And Luna isn't particularly sensitive as to how she comes across to others. This combination leads to a natural sort of intimidation whenever there might be a difference of opinion.

When Nexus is giving his presentation, Luna immediately sees a problem. He is claiming to be able to do things which should be impossible (at least to her knowledge). So her first reaction is skepticism. But skepticism doesn't come across benignly to someone like Luna. Remember, she is driven by principles first. So if she perceives a threat, her first instinct might be to show herself as agitated. She wants Nexus to explain exactly how he came across this solution, because more than anything, Luna feels threatened by the unknown variables.

What's even more important here is that once Nexus reveals that it is Discord behind his breakthroughs, she is momentarily shocked but quickly relaxes because, again, the unknown variable has vanished.

Ultimately, Nexus convinces Luna to relax about it and she approves of the project because in her mind, the risks/reward ratio is sufficiently low to continue.

Contrast this with Luna's tour of the memory orb project. Here, instantly she has a bad feeling about the zebra influences. Luna is fully aware of the dangers of zebra sorcery, but this is not an unknown variable. It is something she's familiar with. So the first thing she tries to do is to determine if the memory orb project is currently based on this type of magic. Twilight/Nightwatch explain to her that it was the foundational research, but it is not actually part of the technology.

This permits Luna to relax much more easily about the memory orb project, with a cautionary order to keep a close eye on the usage of zebra magical techniques.

Of course, there's more to say, but I'll elaborate later if necessary.