See I find food fine, I don't get stressed about it but I really struggle with discipline/boundaries/cooperation (without shouting) and I don't really like playing with them. Watching them play is great, joining in is awful. :o
Everyone has a nemesis in parenting. Whether it's sleep, food, playing, illness... don't beat yourself up about it. It is highly unlikely to be as important as you fear. Any time you catch yourself with the mum guilt, ask yourself "Does my DH worry about this? Did my great-grandmother worry about this?" Chances are the answer will be NO. And that means that you probably don't need to either.
For food some useful (guilt free) approaches to follow are Division of Responsibility - which basically says it's your responsibility to provide food, it's your child's responsibility to decide how much of it they eat (and zero is fine). Also Kids Eat in Color is an instagram a lot of people I know recommend.
There is a lot of crap talked about kids and food, those two are OK IMO. Forget healthy vs unhealthy, specific numbers of foods to eat a day, whatever she wants is probably fine. Fruit, bread and cheese is a pretty balanced diet TBH! It has protein, dairy, carbs/grain and plants. That's a brilliant base so even if she only eats that, that's OK. See anything extra as a bonus. I had one child who would barely eat anything and one that inhales everything, so it's really just down to the child and it's totally fine to follow their lead.
I used to do baby led weaning with absolutely everything, even if it doesn't seem finger food-y, there is usually a way. Pick some pieces out of a stew to try, offer bits of pasta with sauce on, at one they are also pretty good at dunking so you can do sticky foods like yoghurt, porridge, etc with a spoon. Soup with toast fingers. Chilli and rice can be eaten with fingers, they can pick out a kidney bean or chickpea or chunk of mince, roll rice into sticky balls or let them have a pile and smoosh it. Bigger foods like jacket potato can be cut into strips.
Chuck a muslin diagonally under the highchair and it catches most things, then just fold it and tip them into the food waste bin (or collect up to recycle into an omelette or something). I used to bring a spare plate/bowl and ask them to put food they don't want on there, which is surprisingly effective. Also, just end the mealtime if it turns into food-throwing-time. Not a punishment, just an OK, you clearly don't want to eat right now, we'll try again later. Experiment with timing meals/snacks before, after, directly between naps in case tiredness is a factor.
As long as you are offering food regularly you never need to worry if they eat nothing at a meal, as they will have another chance to eat soon. Keep breastfeeding, if on formula speak to GP/health visitor about whether to continue or swap to cow's milk, but a child with no health issues will not starve themselves. And with tummy bugs it's really OK for them to eat little to nothing for 2-3 days. Keep the fluids up.
You're doing a great job :)