They are "hotel" ashtrays?

Tell her you don't gamble, you just collect historical items from all sorts of places, and that some happen to be casinos. I mean really, you do colect other things and ashtrays from non-gambling sources.

Someone else mentioned that you won't win the battle. I think that's some very true, good advise. Best you can expect is to explain that you collect all kinds of ashtrays, and leave it.

Appeal to logic is the best you can do, in a polite answer, and let the message sink in. People who are confronted with changing their mind or faced with a debate, will stick to their position even stronger, the more it's challenged.

Or in other terms, the more difficult it is to defend a position, the more strongly many people will defend it.