I had botox when I was 12, in my hamstrings....it does definatley help to reduce spasticity so that the muscles can be stretched. The negatives would be the effects are only temporary, but being that your daughter is so young it may have more lasting effects if you keep using it along with therapy...and also it is pretty painful to have shots put into your muscles, but they would probably put your daughter to sleep (they made me suffer!

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So all in all I would say it's worthwhile to consider... here is a website
http://news.bbc.co.uk/1/hi/health/2910111.stm