i think you should keep shimmer to the face minimal since she might sweat and the lights are focused on her.. put on oil free primer, foudation with a brush, concealer, then set her face with translucent powder...or powder in her shade... (if she has dark skin, the translucent powder Will make her look ashy) add it THICKLY to her face, concentrating on under the eyes, tzone, chin, or wherever shes mostly oily.. let it sit for a few minutes, then brush off the excess with a thick fluffy brush.. then add blush. and it should keep her face from shining for quite a while And keep her makeup from melting off...
i think you should focus on the eyes more than the lips since she will be singing .. im thinkin if she has bright lips, or dark lips, you dont wanna keep on touching it up all the time so i suggest do a neutral lip.. the eyes.. maybe a smoky brown.. or neutral lid with a muted black like SMUT to contour so it wont be too dark..
i hope this helps and good luck!