I want two pet rats really badly but...?

I currently have two dogs. Also, I've had a bunch of guinea pigs over the years but my last one just died about a week ago :'(. I asked my mom if I could get pet rats (we already have a suitable cage, toys, food bowl and water bottles...so we wouldn't need to buy anything) and she said I couldn't, even if I paid for everything :( When I asked why, she just said we're done with small, furry animals. Even if I wanted another guinea pig or a hedgehog, hamster, rabbit, ferret...she said she would still say no. But she won't tell me why. I've bee cleaning my house like crazy and being super nice to everyone and helping out and everything to try to convince her to say yes for a few days now (but I haven't told her why yet). The next time I ask her, I am going to set up a cage with stuffed animals with name tags (presumably my future pets) holding gift cards, a rat fact sheet, etc and there will be a flower in a pot in the cage, too. I will make the pot and plant the flowers. I will give all of this to her as a gift (aka bribery). How long should I wait to do this? Do you think it will work? What else can I do to get her to say yes?