How often do you normally worm her? If it's every three months I don't see the harm in making it four months if you *didn't* give it to her and if you *did* give it to her then to worm her in a months time means there would be a month between doses which is fine. (the dosage for kittens is every three weeks up until they are 4 months so defo won't hurt Snooch to have a dose a month apart).