You need to tell her because if you don't you won't be able to have the fun arguments about how much money you have wasted buying coins, or the arguments about it losing value but you are still buying it. Or the arguments about how it has gone up by 10cents and why aren't you selling it? Then you would miss out on all the discussions about what inflation is and how it works etc.
On the plus side once you tell her that you have some she will lose all interest and her eyes should glaze over, if not, try and explain the difference between an MS69 and an MS70, that should do it.
Once she knows you have some, you will have no further troubles adding to the stack, one lump of silver looks very much like another and provided you can get it into the house without detection then you can do what you want with it. The only problems come when you say you need a new safe, or more cupboard space to keep the same amount of silver in.
Never keep it all in one place either, for some reason my wife thinks I would like to keep all my silver in one place, instead of the pile for putting in albums, the pile for putting in 2x2s, the pile for chucking in the box, the pile for cleaning, the pile for sorting, the pile of damaged coins, the pile of coins that I need to find out more about , the pile of coins that I don't know what to do with. These should be distinct piles but every now and then I come in to find several piles have been amalgamated to make room on a table for something. Anyway, as long as she never finds all the piles you should be fine.
If you are concerned about future splitting of the proceeds just make sure each purchase includes a piece of jewellery for her and an equal amount of metal for you, by price or weight. That way when it comes time to split she has already received her part. Or if you stick together, you still have plenty of cash in PM.
I don't think you have to get married and divorced do you, just 12 months living together in common law should do it, I would keep quiet about it for a year or so, just in case, or at least, limit the amount you talk about it, you wouldn't go on about stocks and shares and expect anyone to be turned on by that, that's how some people feel about silver!