Sadly workplace bullying is difficult to prove as it requires colleagues to go out on a limb on your behalf. Consequently many excellent workers leave their place of work through bullying. It isn't right, and it is one reason why joining a union is a good idea if you are on low pay.
The legal position as far as references go are explained here:
https://www.gov.uk/work-reference
The thing you need to know is whether the job that you left included an agreement to provide a reference.
You might also track down the previous manager and ask them if they'll act as a referee.
If you quote your current lady as a manager and she refuses to give a reference she looks an @rse, but if a previous employer provides one you're in with a chance.
However, is the lady actually giving you a bad reference? If this is inaccurate then she is liable.