If the gift did get lost somehow (not likely), what could be done about it at this point anyway? Let it go-two rudes don't make a right. ;)
This... Yes, rude if she found them and didn't at least acknowledge, true. But calling her out is also rude, and if somehow she tossed them while doing laundry, she'll be embarrassed plus still out the gift cards.
Bottom line, there's no upside to asking about the gift, since it's not like you could get a refund if she threw them out somehow... Sorry that she didn't acknowledge, but I am confident she was super grateful although she didn't say so!