First, make sure she's actually incredibly good-looking from the get-go, but don't let her know that until she's yours.
There's nothing more dangerous than a nobody who threatens your sexy way of life by being sexy without flaunting it. Now's your time to be her shepherd.
Make sure that she's the only person in the world who doesn't know what contact lenses are.
Tell her the science hasn't been created yet. Then, when the time is right...give her the gift of sight.
Get someone very mean to aggressively brush and/or straighten her hair. Don't let her do this by herself.
I repeat: Do not let her brush her hair all by herself. First it's brushing her own hair, then what's next? Getting bangs without your permission??
Throw away all of her clothes, then buy her incredibly expensive new clothes that she can't afford to dryclean.
This will foster a codependency that will ensure that she doesn't feel pretty until you say so.
Get someone to wax all the hair below her eyebrows until she shines like a prepubescent seal.
She'll be whiny and whimpery for a few days -- that's to be expected. Do not speak to her until the redness has gone down.