Margaret Peregrine is a high school sophomore. Most of the time, she's either at school, at the school robotics club, at the school chess club, or doing schoolwork. Today, she's cleaning out her late great-grandmother's attic.
Giggle. "And if anyone objects you'll just be awesome at them until they give up. Oh, speaking of which, did you want to do that magic interaction test this week? To find out if your sphinx stuff has any side effects we don't want?"
"Yeah, that's a good idea. How do you want to set up -"
"I think the normal way for medallions, including the wake-up spell, but also I'm concentrating on suppressing anything harmful to you? Actually, we should check first whether I can work on people other than myself at all. Do you want to try turning invisible while I try to stop you?"
"Sure." She produces a scroll to this effect and offers Margeret her hand.
Margaret takes her hand and concentrates on not letting any invisibility happen.
Bella recites her Spanish incantation for it and does not turn invisiible!
"Okay, so it looks like I can interfere with magic I'm not personally doing. Want to try with a medallion now?"
"What are you going to do, sphinxify me?"
"Huh? No, I meant we try making a medallion like we normally do and I try to suppress anything harmful about your magic. I guess I could try suppressing your medallion but I'm worried it wouldn't start working again afterward."
"Does that ever happen with things you suppress?"
"No, but I've never tried it on anything that complicated before, or anything that needed sphinx magic."
Bella nods. She goes and gets ready to attempt a medallion.
And when they get to the part where Bella does her thing, Margaret keeps an eye on her suppression-detector and concentrates on not wanting any harm to come to Bella ever for any reason. It's not a difficult thing to concentrate on.
Bella's thing goes off completely normally and she passes out.
Huh. So either the passing out is normal and healthy, or she can't affect sphinx magic. Margaret shares these hypotheses when Bella wakes up.
"It doesn't seem likely you can't affect sphinx magic at all. There was an entire war, it lasted a while."
"Well, I'm not sure it would have been much use in combat, the range is really short. I guess I don't know how much of the war involved melee fighting."
"I mean, if I did ranged sphinx magic it wouldn't touch you if you didn't want it to, presumably."
"Oh, yeah, maybe. Or ranged magic with a diagram, for that matter. Now I'm wondering how it handles stuff like scrying, where I'm involved but there's no perceptible effect on me."
"Huh, I don't know. Maybe if you touch the diagram it still counts?"
"Maybe. I was also thinking about someone else trying to scry me from a ways off while I'm thinking about not wanting to be scried."
"Oh, that's a good idea, I don't know how to expect that to turn out."
"Would you like to help test it? I should still have a copy of the diagram."
"Is your incantation in Spanish?"
"Oh, that's right, you've never used it. I can write down the English version and you can translate it later if you're interested?"