She doesn't need it - and shouldn't waste time trying to get it. The purpose of a P45 is to ensure that the new employer knows how much tax has already been paid by the previous employer and what the tax code is - without a P45 the new employer has to assume that the tax code is whatever the default is and that no tax has been paid so far - commonly known as "emergency tax", so you pay more tax than you expect to.
However, it's only relevant within a tax year so after this length of time, it's of no use anyway.