Hello! Personally I would say that the ideal is more than one, as they are social creatures and studies show that bonded rabbits are generally happier and choose to spend most of their time together. Is your bun outdoors or indoors? Again my personal preference would be that if you have one rabbit, ideally it should live indoors so at least it gets plenty of interaction with people. It's very difficult to do that with an outdoor bun which will be alone for probably 22+ hours each day. In my experience, bunnies have seemed fine on their own but when I have bonded them and seen the difference in their behaviour afterwards, I realise how much happier they have been when they have had a friend.
What are your parents concerns with two, do you think they would be open to persuasion or would it become difficult to afford? If not, try and give your bun as much space and as many things to do as possible so that she has plenty of things to do and doesn't get bored, plus a really cosy area to sleep especially in this weather.