Okay, let me see what I can suggest.
You have a major basic problem, which is that you are a magician who blows chunks at casting spells. This has to be fixed.
Yeah about spellcasting: I thought her to be a mostly (if not completely) conjurer type. So basically she doesn't sling spells around, but instead flies with her spirits (Both real as well as astrl, that's why it's magician, not wiz adept).
As you see I didn't put any thoughts into spells at all yet. Is a pure conjuror even possible? Or should she go for spells, and if yes which?
You have Artificer as your mentor, which is rather odd as you don't have Enchanting.
^^ you directly dived for the weirdness. Yep, I did choose artificer, despite her being the diametral opposite. Why? Roleplaying reasons. In-game it wasn't her choosing artificer, it was artificer who said: "Oh, what an interesting weird raw material. Let's try if we can build something useful (read tinkerer) from it. THAT is basically the great plot hook behind her, the "friendly big brother" that turned her life upside down.
You need to, first, cut stuff, and second, afford basic "I can cast spells" things
.
See above. Which spells do you consider absolutely necessary, and at what level?
First and a half, though, you need to decide what you want to do about that 1 body. 1 body will, inevitably, get you killed. You can:
a) Buy more body with your first 10/25 karma, and try not to die until then.
b) Buy more body now.
c) sustain Increase Body on yourself, and cry if you enter a Background Count.
Well, this char isn't intended for a combat heavy campaign, but rather for a "char development" campaign, where the story/development the chars are going through is the most important.
The reason why I did place body at 1 (away from my answer I'll write below this post) is that she is a very young pixie, and "frail" even for a pixie. Given that 2 is average for pixies ... this doesn't leave much room to navigate. Of course once artificer is done with her, she'll pobably be body 2 (3 stretches it a bit far, doesn't it?)
Things you need so that you don't suck at spellcasting:
Spellcasting (Specialization) 6(
Summoning (Specialization) 1(3)
Counterspelling 4
*nod* sounds perfect for a spell slinger. Why do you take summoning at such a low level? As said, I envision her more as a spirit walker. Is that soo unwise compared to a spell slinger?
Some spells!
*nod* illusion spells probably, right? What do you suggest?
Unless you do not care about combat in the slightest, you should have a Force 3 health sustaining focus and Increase Reflexes like all the other kids.
Hmm, she is right out of her windling village. I didn't read it like there was a prosperous talismonger industry in Brocelande. Would this still make sense? Or would it besomething to aquire asap?
If you can possibly afford it, you should get Restricted Gear for a f4 power focus like all the cool kids. It is more important than basically anything else that improves your magic and you should only skip it if you want to deprioritize magic in general in favor of other skills.
As above, would she even have access to such a thing "in the fairy forest"?
You probably want at least 1 in Enchanting and Binding as a Possession tradition with high Charisma, but they aren't quite as vital as the above.
As you might have guessed, I didn't decide fialy on the tradition. I did choose witchcraft, as it comes closest to what I imagine. Does it even make sense, or is druidic (which is not possession based) more sensible? What are the pros and cons for a conjuror concerning possession?
Never take Conjuring. Banishing is crap.
*nod* So the group is out.
Ritual Spellcasting is not all that vital as a PC. You don't ever want Sorcery because you want Spellcasting 6 so bad.
Same as above.

You should almost certainly have, as well,
Assensing 1
Perception 1
Infiltration 1 (I'm not sure you want Disguise or Palming. Maybe Shadowing, but actually, spirits are really, really good at following people by doing it on the Astral).
Influence 1
*nod* What about astral combat? Any sense in it in a "don't fight" char?
You probably do want more of these, but you need to be functional and under-budget first.
*nod* I thought so as well

So basically scratch most/all groups and concentrate on the important skills?
Things you need to cut:
You cannot afford all of those stats. Not even close. Some of them have to go. In particular, you don't need nearly that much Agility - you aren't making physical attacks. If you want more Infiltration, buy more Infiltration, not the Agility.
I was going for full agi to be able to get away from fights. IIRC dodge is based on AGI as well, right?
You are an Intuition tradition with more Charisma than Intuition. You could have less Charisma, or you could pick a Charisma tradition instead. Intuition is useful anyways because it affects so many things.
*nod* As said, the tradition isn't final (maybe I might even develop an own windling tradition with your help, but that's not important yet). Charisma is as important for her as she is a conjuror and a face. So which tradition would you suggest?
Edge is cool, but not at the price of sucking at your core skills.
*nod* Edge is probably the best place to cut cost. I softcapped it, due to her being a "windling" for me -> they have an edge advantage.
Asd you see, it's truly a VERY first draft, and there is still a lot possible. I'll add in your suggestions in the next break (need to use this one to answer the next post).