I'm a rubbish cook and find catering hard work (I'm now sahm so it all falls to me atm). I also hate cooking meat (squeamish) so I thought some of my meal ideas would help (low effort and no meat!).
To be clear, she's not vegan? Just doesn't like egg and is veggie? (If she IS vegan, I recommend the Pure website as they have great and easy recipes. Thai curries are your friend too. Plus CoYo yoghurts, soya choc puds, Free From range at Tesco, and those delicious raw fruit bars (Nakd) which I scoffed when I went dairy free and lost lots of weight, the choc orange one is like eating brownie yum!).
So my low effort veggie meals are:
Gnocchi. One meal is gnocchi (ready made natch) with roast butternut squash, ricotta and spinach (just add to gnocchi pan at the end). The other is roast asparagus with gnocchi and sundries toms (mozzarella or Parmesan too if you want).
Nigella's roast cauliflower salad with hummus and flat bread
Pancakes (no sugar) with cheese or cream cheese and veg (broccoli as my dc will eat it, but you could grate courgettes and carrots and then lightly sauté before mixing in cream cheese)
Massive mushrooms or slices of butternut squash with halloumi on top, roasted (mushroom or squash first then more cooking with halloumi on top), stick em in pita with slices of tomato
Couscous with lemon juice, chopped black olives and red onion, and a grilled courgette and either halloumi or feta on top
No eating rice is a pita. But she could try noodles that aren't wheat (just for a pasta break!) eg rice or buckwheat?
Tesco also do frozen stir fry veg which I'm gonna do for ds who loves Chinese food but I always end up wasting fresh ingredients when I do this normally.
Veggie burgers, nut roasts, veggie fingers are all good esp with chips!
If iron is a concern try and sneak spinach into everything. My dad makes me lush spinach pies with spinach, feta or cheddar, sultanas mushrooms and pine nuts. If she is not morally opposed to egg you can pop some in here to bind up the ingredients and it won't taste eggy, iyswim.
If she has as you have said had a hard time recently it might be a lovely thing to do together, to try out new recipes and cook together. At 16 it's the perfect time to learn and nice to have a thing you can do with her?
Please don't punish her weight gain by not getting her clothes that fit :-( weight gain IMO is often caused by low self esteem and I have never managed to lose weight by trying to fit into tight clothes. Tesco do really nice things and are not expensive, maybe at least get her some jeans and a couple of tops - again it would be a lovely thing to do together.
Obviously I don't know the full story but it sounds like money is tight and you have a lot on your own plate (scuse the pun!), OP?
if so, please remember your dd isn't really old enough to understand all of that yet. I hope you find some tasty things that you all like to eat and that this brings you closer to your daughter.