Same here, granted, mine have a tablet and not a phone, but Kids Mode blocks everything nasty so far. I don't think your problems are based on the child beeing autistic or the like....all ten year olds share numbers and spend the day on whatsapp and the like if they can, chatting like mad. Some stay like this for decades. Whatsapp may actually work well, as it'll work on your home WLAN for free, not eating her dataplan.
