I think the best thing is to ask her as you may be doubling up on something she's already got. I know it's always lovely to give a surprise but it might not end up being a good one.
Other than that, crystal wine and water glasses are useful and don't forget the wodka glasses.
Could you perhaps wait until you're there, see what she's got and then choose? Sorry, I don't know if Polish wedding etiquette allows this. You'd lose the surprise element of turning up with a gift under your arm, but wedding gifts are often, at least in Britain, chosen quite unsentimentally, to fill a gap in the happy couple's household.
if you are looking at spending that much why not book them a weekend break somewhere in a posh hotel or health spa, it is something they will remember forever, you can always buy them something small too just to wrap up
Why not give her the money instead; this way she can buy whatever she'd need. Or tell her how much you intend to spend and take her to the shops and let her choose her present.