If I remember correctly, there's no problem with using like as a preposition. The controversy comes up when people use it as a conjunction.Hello. If I remember my English grammar correctly it should be: treat as...(as in, treat her as if she were a diva) but in everyday colloquial English you always hear: treat her like...
I would agree with this. Diva can also have negative connotations and be taken as an insult, so be careful. In the context of a husband or wife, treating her like a princess/queen/royalty would probably be better.Diva has a quite specialised meaning (see WR Dictionary), so you would only treat her as or like a diva if she were a celebrated opera singer.
In the absence of further context, I would prefer 'treat your wife like a princess' (make her feel special).
If forced to create a difference, I would say the difference is something like this:I treat my dog like my sister.
I treat my dog as my sister.