It all depends on your budget. The traditional gift for the 13th anniversary is lace. Perhaps you could return to where you spent your honeymoon and buy her some sexy lacy lingerie, remind her she is still that beautiful woman you fell in love with.
You could also renew your vows and buy her a dress with lace attached or lace around the boquet.
Or a lace engraved crystal vase and 13 red roses, one for each year.
Happy anniversary in advance, what ever you decide I hope yuou both have a wonderful day.