How do you teach politeness in toddlers?

besides modeling it. My 2 yr old is very shy even with extended family like aunts/uncles/cousins so she never gives goodbye hugs, kisses, etc. She is usually hiding behind me. While I am fine with that from her, the problem is my 3 yr old. I think that she is copying her sister. When ppl ask her for a hug or kiss she says no. Sometimes when ppl speak to her she ignores it all together. I'm not sure what to do, I don't want her to come off as snotty or rude....but I don't want to force her to give kisses....