She needs to approach this situation very carefully as the last thing she would want to do is to make matters worse.
- Call her old boss and ask if she'd be willing to reach an agreement
with you on what she'll say to future reference calls. It's at least
worth a shot—the worst that can happen is that she'll say no. When
you call, say something like this: "I'm concerned that the reference
you're providing for me is preventing me from getting work. Could we
work something out so that this isn't standing in my way?"
- If she feels that the reference her boss is providing is factually
inaccurate, skip her and go straight to her old company's HR
department. Explain that your boss is giving an inaccurate reference
for you and that you are concerned she is standing in the way of you
obtaining employment. HR people are trained in this and will be
familiar with the potential for legal problems, and will probably
speak to your old boss and put a stop to it. (If it's a small company
and there's no HR department, I would advise contacting the old boss directly and
politely explain that she's exposing her company to legal risk by
defaming you and jeopardizing your ability to gain employment.)
- If all else fails, she may need to simply warn prospective new
employers that the reference won't be a good one. And you do want to
give this warning, because it allows her to provide context and
framing for what they might be about to hear. If you don't, they may
never tell you that the reference is why they rejected you, so the
time to speak up is before they place the call. How she explains it
depends on exactly what's behind the bad reference, but her goal should be to put it in the best possible light. For instance, if her
relationship with your boss soured after a particular event, she
could say something like, "By the way, I had glowing reviews from my
boss at that job, but our relationship became strained toward the end
and I worry that it could colour that reference." She would need to be prepared for
questions about what caused the strain, of course.
If you think the statements made in the reference are untrue and believe that it then unfairly harmed your future work prospects you may be able to take the person to court for ‘negligent misstatement’. To do so, you must show that:
The information in the reference is misleading
Providing this misleading information has had a negative effect on
your future employment.
Your employer was negligent in providing a reference.
Alternatively, if you think there is an element of discrimination involved, you can bring your former employer to an employment tribunal.
As you are in the UK I would strongly advise you to get her to visit this site for further information and what her rights are.