Wouldn't her first step to be to get a copy of her birth certificate (long form, with parents details) from Zimbabwe?
http://www.moha.gov.zw/index.php?link=rg_death_births
Does she know where in Zimbabwe she was born?
The British Embassy in Harare might be able to assist.
Also perhaps try the National Archives to get records of her entry to Britain:
http://www.nationalarchives.gov.uk/sear ... ration.htm
And once again, try getting in touch with Polish emigre groups who may have dealt with similar problems? Can the Polish Embassy provide any contacts?
Who administered the refugee camp? The Red Cross? Perhaps they have records?
Sorry if this isn't what you want to hear but there is going to be a lot of work needed to track down some of the basic details - such as the birth certificate. You can only start even thinking about the situation under the law, once you know the facts.
She could also, in parallel, apply for settlement in the UK under the 14 year rule for unlawful/undocumented stay. That won't get her a passport anytime soon, but at least will resolve her immigration status.