Douglas' verses were re-written by Lady John Scott (who is also credited with the tune) around 1834-5. The poem was not written in 1685, as so many websites have it; Anna Laurie would, so far as I can tell, have been about 3 years old at that time. There's so much nonsense and half-baked misinformation circulating that it's hard to be precise, but I'd place the poem in the early years of the 18th century; she married (somebody else) in 1709.