My sister is very immature?

I have a sister who is 10. She still sucks her thumb. She doesn't brush her hair , she likes to 'stuggle' with my mom? , she has to have my mom help her with, TAKING BATHS, brushing teeth, putting on shoes and socks, all of her homework, putting her to bed until she falls asleep, packing up her backpack, and SO much more. She also does this weird thing and she picks her neck. She said she can feel little balls in her neck and it is leaving some rash. She SCREAMS all the time at home and is SUPER mean. She does that in public too, but when someone in public talks to her she gets so shy. She cant even order a meal at a restaurant to the lady, but she yells and crys when the lady leaves even though everyone can hear her... Well yeah, I know that is so odd, but she doesnt really have mental problems. She just act so childish. What the effff is wrong with her? Is she ever going to change? How?