Gym ball, gym ball, gym ball. Use your birthing ball if you had one.
Loads and loads of sitting on it and balancing (you hold her legs and she can lean everywhere - even right the way back if you hang on - hips better than thighs) and then wheelbarrow type leaning on it and rolling and rocking, and lifting legs and arms 'superman' style.
Gym ball, gym ball, gym ball....
Dd2 spent hours on her gym ball.
The other thing was great in the longer term was ballet. She started a class at 4 before she could stand independently (she could walk but had no standing balance because of her tone). Get a toddler ballet DVD and get her to hang on to a chair back.
Balancing games whilst learning to catch - standing with one foot on a step, kneeling, kneeling on one knee, etc etc. and throwing obv. Get a great big bobbly therapy ball, or one with knobbliest anyway, for better grip.
Lie on back and get a majorette baton from the pound shop (sparkly ones always good) and play 'the grand old duke of York', moving the baton (held across the body int wo hands with straight arms) up to the top of the hill (floor above head) and down again (to legs) keep arms straight! Oh, and buy spares, because every sibling in the land wants to lie on the living room floor and play too!
Get the cars out. Wheel them up and down the therapy wedge, push them around the living room floor.
And (TA da) buy a huge trampoline with a net. Dd2 couldn't stand on ours at first, but it was great to watch her get more confident, and the safe environment and constantly changing muscle needs mean that they are great for core strength. 