Restaurant serves Celiac gluten

Hi,
A friend of mine recently went to a restaurant on Sunday and ordered a steak meal with gravy. She has celiacs disease, meaning that she is not able to consume gluten as it makes her quite sick as well as giving her severe stomach pains. She specifically ordered a meal that was gluten free and, as she had eaten there previously, presumed all was well. After finishing her meal, she began to feel the symptoms of gluten consumption and approached the staff who again confirmed that there was no gluten in her meal as they had marked it so on the order.
After talking to the chef, she discovered that the restaurant had run out of its gluten free gravy and instead of informing her, sent someone to the local supermarket and bought gravy that was not in fact gluten free. It was this gravy that was served to her.
After this, she suffered stomach pains throughout the night and went to see a doctor the following morning. She continued to suffer severe stomach pains over the next week, as is common in cases of gluten consumption for celiacs.

The restaurant manager apologized on the evening and she received a call from the owner the following morning with the offer of a voucher for a meal and a one night accommodation voucher, which she refused as she did not believe that was good enough for the pain and docter's costs she footed as a result of such negligence from the restaurant.

What are her options? Preferably, she would not like to go to court due to the legal costs involved (would it be worth it?).

Any help would be much appreciated.
thanks

I think that if the menu says no gluten in this meal, then that’s what it means, NO GLUTEN, and then that’s what you trust. In my professional opinion, l believe this restaurant is a big stuff up. It is not up to the customer to be responsible in telling the restaurants how to do their jobs.