The aggression is likely to be learnt behaviour and may well have developed because her hutch was so small, anyone putting things e.g. hands in was seriously invading her space!
As she's so over weight and has a history of lack of exercise you need to be careful about how much exercise she has. It's tempting to give a giant space and let her enjoy freedom but she may not have the muscle or bone structure to support binkies and running about at the moment, so increase gradually. Even a normal sized hutch will be a big change for her.
Generally just feeding the correct diet will bring weight down, so plenty of hay and only a small portion of high fibre dry food. How does she feel about hay? If she doesn't move much a treat ball for the dry food may encourage some gentle exercise.
You want a slow and steady loss rather than getting weight off asap. So weighing once a week and as long as it's going down even a little bit you are doing right.
For the aggression, I would give her a week or so to settle and keep your hands out of the hutch. You want to avoid triggering the behaviour because that reinforces it - she lunges & you back off = lunching works. Instead get her used to you being around, delivering tasty things but not trying to touch/grab her. If you need to do something in the hutch with her in it then, presuming it's got a bed divider, you can slide a spare piece of board across the entrance and close her one side whilst you put food or clean the other.