Be aware that flower girls are often matching the bride so can be in white/ivory even if bridesmaids aren't.
It is a very obvious bridesmaid/flower girl dress. It's also white. Some brides would be really upset. Even if the bride isn't the chance of a mother etc being offended is high. So if you put her in it expect to be told by guests that:
You are attention seeking.
That you are trying to make your child seem like a bridesmaid.
That you are disrespecting the bride.
Honestly I would just buy something else if you are able to.