I live in the Netherlands, and it is a given that there is always a surprise gift to the bride and groom on top of the gift list. I have been to weddings where we had to bring a cooking recipe with a bottle of wine to have with the meal, that sort of thing. On my wedding day my surprise gift was "seeds/bulbs or something from your own garden that means something to you that the bride and groom can put to use in their garden" I got married in September, so received loads of bulbs, I received loads of bridal flower bulbs, I had never heard of this plant in the UK, but they are a pretty white flower..
maybe she could give seeds from a flower in her bouquet with simple instructions of when/where to sew...
I must just add that the instructions to my guests was to not present the seeds in their original packet...I have to say had my car been stopped by the police that night, with lots of seeds in suspicious packages, my wedding night would be for another forum...
Have a wonderful day...