If it is stress and struggling to cope with death and if she is genuinely worried/concerned about not eating (and some people do react to stress with lack of appetite/inability to eat) I would start by giving her easy ways to prevent her losing anymore weight without having to eat loads. Don't pressure her to eat proper meals or meals at all, just small, regular high calorie snacks.
Would she have build up drinks like complan - a couple a day to start with.
Other stuff she could try are smoothies, a handful of nuts or trail mix, even biscuits, flapjacks, cereal bars, cheese & crackers, toast with peanut butter. It only needs to be very small amounts so not overwhelming - try and get the frequency rather than the portion size up to start with.
Look at what she is drinking as well as a way to get calories in - on top of smoothies, build up drinks - hot chocolate made with milk, milkshakes, tea/coffee with milk and sugar, fruit juice, even fizzy drinks at a push.
Get her to take a multivitamin and if it doesn't contain iron then an iron supplement as well (spatone is an easier iron supplement than tablets). Poor/reduced diet can lead to anaemia which in turn can lead to reduced appetite and turns into a vicious circle.
Encourage her to see a dr, though I appreciate she is an adult so you can't make her. Exercise - even just walking helps with stress and may also help stimulate her appetite.