Good for her for being compassionate and having strong morals I say! But I get your concerns on the dietary front.
If I were you I would buy some vegan recipe books and follow some vegan recipe accounts on Instagram (if you're not on Instagram, she will be I'm sure!). Sit down with her and go through them and work out the sort of things she would eat.
Vegan food is great in that it keeps for ages in the fridge. For example, I roast a huge batch of veg (aubergine, red pepper, asparagus, courgette, etc.) and it will keep for a week in the fridge. I also make a huge batch of pico de gallo (chopped tomato, jalepenos, coriander, red onion) which also keeps for a week. I then make up "Buddha bowls" - roast veg, pico de gallo, roast potatoes, salad, avocado, lentils or black beans (both from a can), hummous, sprinkled with seeds - the variations are endless! - and have them throughout the week, interspersed with other vegan meals like green thai curry or a pad thai (which can be done in 10 mins), or pasta with a tomato sauce, olives, roast aubergine and basil, for example.
I became vegan about 5 months ago and feel an awful lot better for it and am now much more adventurous with my cooking.
The two things to watch for are iron and B12. I put a sachet of Spatone (natural, iron-rich water from a spa in Wales) in a glass of orange juice in the mornings, which sorts the iron. For B12, I eat marmite (very rich source of it) on seeded toast every morning and have a glass of Berocca a day (full of all B vitamins).
Hope that helps!