If you know enough about ritual theory, you can develop new spells. Unfortunately Jawbreaker does not know enough about ritual theory and this will have to wait until Overbite's brother can teach her. But he can familiarize her with several rituals. Once she's performed the rituals and gotten them down firmly he can help her start abridging them, starting with steps that occur in a lot of different rituals.
For practical reasons, Promise would like to as much as possible abridge rituals into actions she can often perform even while under heavy orders, such as blinking, breathing, and various actions that are part of keeping her balance.
...Actions like that introduce a risk that she might do magic accidentally, but if they're careful and creative she can have something like breathing to a certain rhythm instead of speaking, and blinking in a pattern. Does she anticipate relative freedom of facial expression while under heavy orders?
She can't wiggle her ears. Rolling her tongue will be noticed; irregular breathing won't. She could usually tense muscles that didn't complete visible motions of their own? Clench her jaw, say.
"...Huh. I never noticed you can't roll your tongue without opening your mouth. You can clench your jaw, but if you were in the habit of doing it otherwise you'd need to break it; if a gesture means magic to you then it will do magic whenever you do it. That's one reason most magicians prefer grandiose gestures and nonsense words; you're unlikely to do those without meaning to. Your situation is different, of course, but that does mean you'll need to be more careful."
"Maybe the entire stealth idea is worthless anyway. If someone clever gets me I'll be under a general order that won't let me do magic regardless."
"Maybe I should wait until I've picked a complete spell I want available under those conditions and assign shortcuts to its components then. Everything else can be a word or a gesture."
The silence ward is incredibly complicated. If you do it just as a ritual it can take up to a week to do. But you can abridge things indefinitely if you work at it enough--these steps are all abridged as gestures and these gesture sequences are abridged as words and these word sequences are abridged as another gesture. Most magicians are limited by their ability to create and remember distinct abridgements. If she works very very hard and is good at remembering things, she could eventually cast a silence ward by clenching her jaw.