Hot weather

I know how to dress Elle for cold nights...but what do I do now that the weather is changing? Do I still put an undershirt/onsie under her cotton pajamas? Last night I put the ceiling fan on in her room with regular pajamas and a onsie. Is that ok? We will install her air conditioner when it gets a little warmer (probably over the weekend because we have to clean it and put a filter in). What temperature should I set it to?