I would make the effect very difficult to turn off by "dressing" yourself in an illusion. Maybe you have to renew the illusion every Diameter since the invisibility effect recasts itself periodically? Same for painting yourself with paint or other mediums: Recast = paint becomes invisible,. so you are still messy and dirty, but invisible. Even if you "dress" an illusion, you would perceptibly BLINK every 2 minutes in a really noticeable way (puff of smoke, lights or sound that attract attention to you?). This can be really annoying for social interaction.
Stuill, being a magus, this can be avoided with certain easiness. Unless you make it count as a BIG flaw or a driving force for him/her to go out and try to get rid of the curse, I would say minor flaw. Yopu can build a pretty effective spy/assassin/burglar with this curse.
The best way to avoid this would be a kind of image from the wizard torn, but it being a CrIm effect to create yourself nearby.
Or you can have this effect kick in and out at random, depending on the SGs desires, so it is really annoying. And then it would be a Major Flaw for sure. Irt can drive both the character and you totally nuts After all, we all know that most SG are dark faeries that get vitality out of frustration
I would make this a fog-like effect , so that all magic must be used at Touch Range (or Personal).
This is an effect that is otherwise invisible to anyone without Second Sight.
Your Maga can see normal things without a Might Score or Magic Resistance as if through a light fog.
Her spells that operate at Range greater than Touch or Arcane Connection have to Penetrate a certain value , perhaps.
The shroud/fog that covers her is similar to a Mentem effect (with Animal requisite) , therefore invisible to normal sight.
The Gift operates as normal.
Elegant solution! I like it Makes "dressing as an illusion" useless since it is a Mentem effect. Your eyes register the maga, but your brain refuses to acknowledge her.
However, the effect needing to penetrate has the unwanted consequence that Magi can see her with no problems. The alternative would be to make it penetrate with a total of (say) 250, so that no magi can see her without spells. Magical beings are not affected by Mentem (usually) so they are immune to this effect.
Let imagonem that are too close to the magi become invisible as well(or the part of it closest to the magi). On the basis of the "objects<size 2 that are touched also become invisible (so putting on a cloak is no answer)" rule, but affecting more because its "just illusions". Like, any part of an illusion within her near presence/"aura" fades out as if overwritten by the "aura". So anyone using illusions near her carelessly will have a part of their illusion fading where she is.
That makes a sort of twisted sense while keeping the problem, even adding a bit too it.