JustJess

I have to do core strengthening exercises for my back rehab - these are what I do SO far:

'planking': from lying on stomach, push up to rest on elbows and toes (feet almost together), hold for 30 secs/5 reps (longer if you can, I suppose).

leg raises: all while holding stomach tight -one leg bent, the other straight with foot flexed, raise straight leg up slowly, pause at top, and slowly lower, never resting on mat. 5x5. With ankle weights at a comfortable weight. Same method for following positions as well.
- on side, move bottom leg in front, and raise top leg while straight with foot flexed. Keep leg in straight line with body - keep body line straight too.
- on side, bend and rest top knee on a soccer ball or something, and raise bottom leg with leg straight and foot flexed, pointed towards the ceiling, as much as you can. the position should be farther back than you think.

raises: lie on your back with your legs bent, and squeeze a small ball (softball sized?) between your knees. raise your hips off the ground until your torso is in line with your thighs and hold 30 sec/5 times (or longer if you can, I guess!).

Also, just standing up straight and keeping your stomach taut will build things pretty amazingly - you'd be surprised at how strong the average woman's stomach is, just because of doing that!
Good luck!

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My heart knows me better than I know myself, so I'm gonna let it do all the talkin'.