Get the nylon splash pants that have the thin liner to them - it seems hot but they are not that bad and then sew on denim or twill patch the bum part and patch as it wears out. It will give the bum scraping support and keeps the legs from getting injured. In hot weather remove other clothing except diaper and just wear the splash pants when going out to play and remove when in the house. Have other ones you use for in the house. Make sure she is wearing pants that move such as sweatpants or leggings and not cotton or jeans that are rigid.

Working with a stability ball is fun for a lot of kids. Hold child in sitting position on exercise ball and bounce her up and down. Gradually move from holding her under the arms to holding her arms as she learns to balance sitting on the ball. Look up information on trunk control and strengthening that skill. That is what she needs to master before she will be able to stand/walk.