Fenna is the daughter of Hestefan the Singer, and his main apprentice. When young Mitt is beginning his journey along the green roads in pursuit of Noreth Onesdaughter, one of the first events he witnesses is the wreck of Hestefan's minstrel cart at a ford, with the horse half on, half off the slippery underwater stones. Mitt's companion Navis shoots the horse, which has broken two of its legs and is crazed with pain, and when the chaos of dismantling the cart and its couplings and getting everyone and everything out of the water is over, it appears that a young lady who's identified as Fenna is injured, and must be taken somewhere for doctoring.
Later it turns out that Dagner Clennensson is in love with Hestefan's daughter Fenna, but that appears to be another story entirely.