Why is my daughter so shy?

She's almost 4 (in two months) and is so shy. She won't talk to people she knows, like her grandma. If there's other kids at the park, she clings to me, won't let me put her down, cries if I try to put her down, and won't socialize. She's won't make eye contact when people talk to her. She just looks off and sometimes will shake her head "yes" to answer their question (only with someone she knows like grandma). She's starting preschool this month. Idk how she's gonna go. How do I take her when I can't put her down off my hip or she cries? She also has 4 comfort items she always needs, 2 stuffed animals, a blanket, and her pacifier. She isn't potty trained yet and still poops on herself. She also pees on herself if she's in a pull-up but she knows to go in the potty. She just won't. She's smart and can work an iPhone perfect but doesn't know her colors or how to count to 3. She needs preschool to help her but she's so shy. Any help? Also, she doesn't have a bedtime, she stays up till 1 and 2 in the morning. She watches cartoons and sometimes I fall asleep and wake up and look over at her and she's still awake! At bedtime, she says she's hungry constantly and eats 3 or 4 different things and drinks a bunch of juice. Ugh help!