Why do you think maxim asked his wife to dress up as Alice in Wonderland?Do you see any similarity between Alice and the new Mrs de winter?

Maxim tells his wife to dress up as Alice in Wonderland because she is acting petulant, pouting.... like a little girl. This idea is referenced twice, and both times Maxim mentions it as a joke.

Maxim asked his wife to dress up as Alice in Wonderland because she is also sometimes in her own world and even he was teasing her; Yes, i see some similarities between Alice and the new Mrs. de Winter because the new Mrs. de Winter is also sometimes in her own world just like Alice and also she behaves like a small girl like Alice is.