Don't think it matters, she just needs to show that she will be living there with you. You have a rental contract and she'll be living with you as your dependent. You don't think kids' names need to be on the contract to be able to register do you? No, so neither does your wife.
What you do need to make sure of is that you have up to date copies of her birth certificate and your marriage certificate - by up to date I mean less than 6 months old. This seems to be a requirement with many of the cantons, but check with Geneva's migration office or your commune admin office if they need recent ones or not.
This also gives info: https://www.ch.ch/en/family-reunification1/