Can she plank and/or side plank? There are a lot of great core exercises for all levels of exerciser from a prone position.
Plank (lots of variation)
Bear crawls, or alternating hand, hand, foot, foot lifts while stabilizing spine
From standing, warding drills with the ball (i.e. trainer holds the ball, client presses the ball from varying positions) are great.
If you have bands, you can attach a band approx chest high, position the client 90 degrees to the band and have them do transverse rotation. Lots of ways to play with that – anchor height, foot position, direction of pull, etc.