Please, please understand, she is not being rude she is shy.. Big difference and should not be punished or have loved ones assume the worst from her.
"What Is Shyness?
"Shyness is an emotion that affects how a person feels and behaves around others. Shyness can mean feeling uncomfortable, self-conscious, nervous, bashful, timid, or insecure. People who feel shy sometimes notice physical sensations like blushing or feeling speechless, shaky, or breathless."
"Shyness is the opposite of being at ease with yourself around others. When people feel shy, they might hesitate to say or do something because they're feeling unsure of themselves and they're not ready to be noticed."
Some people can also become physically ill.
Please follow your child's lead and help her when meeting other people. Not by shaming or embarrassing her, but by giving her some words.
"Suzie is a little shy."
"Suzy Mrs. Smith said she likes your dress, isn't that nice?" then allow your child to nod. Then you can say, "we thank you, Mrs. Smith".
Some people never get past their shyness and others over time become more comfortable speaking in public, with strangers or participate in new experiences. This is a social situation that needs to be practiced just like reading and spelling.