I dont know what you fancy, but my Mum & Dad has these fabulous genuine Fair Isle sweaters they bought when I wasn't even a twinkle. They are dark (chocolate) brown all over, with a brown/cream/beige fair isle pattern around the yoke and cuffs. I think for that wonderful age of lady, you cant go wrong with traditional, the curved yoke looks great.
Good luck. Get the main bit done so you're not rushing the Fair Isle bit on Christmas Eve