1. You owned half the house anyway, so there's no possibility you could lose all of it.
2. I assume the other half was left to you in your father's will.
3. If this woman (who seems a right b**ch from what you say) thinks she has any right to any part of the estate she will have to make a case based on her dependency on your father. You say she was a companion "in the day" for about 6 months. Does that mean she never actually lived there? - it is not clear because you also say "we lived in the same address".
4. If she was only there for 6 months I would think (even if she was living there) she would find making a valid claim impossible unless she has proof that she spent money on things like the mortgage. Even then, it could easily be argued that she was simply paying what amounted to rent for her accommodation.
5. If you are still concerned, you may need to consult another solicitor.