Both my kids were pretty much on finger foods exclusively around that age. They had little interest in the spoon to start with and by then, they wanted nothing to do with it. So it's pretty common and it's def possible to maintain a healthy, balanced diet without purees.
One thing to keep in mind is that purees are mostly water and finger foods are, well, just food. It makes sense that she eats less when given finger foods because they aren't watered down, KWIM?
Food is meant to be a learning experience at this age and formula/breastmilk should still be her main source of nutrition. I don't know if trying to cajole her into eating more purees is such a good idea...finger foods or baby-led weaning would likely give her a better eating experience. If you really want to keep up the purees, you might try giving her a bowl and spoon of her own and let her have at it...
You can offer anything as a finger food as long as it passes the "mush test:" put it in your mouth and see if you can mash it up with your tongue against the roof of your mouth. No teeth. If you can, it's soft enough for your DD. If roast chicken passes the test, go for it! Other good sources of protein are tofu and cheese. You can even buy large curd cottage cheese and offer that as finger food...a great source of non-meat protein. IMHO, you can offer even more variety with finger foods than with purees, especially if you cook. You can start offering age-appropriate bits from your own plate, which is great for exploring new tastes.