Has she got this document? If it says tenants in common what % does it say she is entitled to? Why - if it was done when he bought the house - was the house just put into his name? It should have been in joint names. If she wants to rely on the document & he disputes it she will have to answer questions like these.
An unmarried partner in her position is normally on very weak ground - she hasn't contributed anything to the costs of the property or the household bills, so unless she is able to get something based on this document she is liikely to have to rely on whatever generosity he has or walk away with nothing much at all.
If there is a document she may well need legal advice.