Well if you already have the tank, what are her objections?
My dad tells me I waste my money; so now I sneak the girls in the house; he doesn't pay that much attention to them so it's ok. My mam told me "no more" but then she smiles and pays loads of attention and feeds them treats lol - she really likes them :)
Take it slow. Start by setting up the tank. Your going to need to cycle the tank before you get your females so you can use that month or so that the tank is cycling to prove that you are ready for a sorority.
Your also going to need to quarantine each female for a period of 2-4 weeks prior to putting her in the sorority tank to make sure that she doesn't have any illnesses so you could start by just getting one or two females at a time.