Gj handling the situation Ai, kept the doll cuz effort was put into it and we cant just neglect others feelings for our lover all the time especially with silly stuff like this.
But i do get where Chie is coming from, shes not upset about the doll but at the realization that shes not as involved in Ai's life as she thought and that other people are doing things for her she doesn't know, a kiss blew it all away though, a "im here with you" i guess, indeed very youthful and pure if that makes her so happy.
Its cute.