The answers above seem to have come mainly from people who've never read the provisions of the Inheritance (Provision for Family and Dependants) Act 1975!
If you'd been living with your partner for a period of two years at the time of her death, as if you were her husband (even though no actual marriage had been entered into), then under Section 1(1A) of the Act you would have the right to apply to a court to vary the terms of her will to provide you with 'reasonable financial provision'.
In considering such an application, the court must have regard to the factors listed in Section 3 (1) of the Act.
http://www.legislation.gov.uk/ukpga/1975/63