The richest sources of protein are animal foods such as chicken, meat, fish, cheese and eggs. However, plant proteins are believed to be healthier because of their lower fat content. Plant protein is found (eg) in beans (esp. soy beans), lentils, nuts, quorn and seeds.
The average adult needs about half a gram of protein per pound of healthy weight.
I got this from a website somewhere, so not sure what the amounts for children are. Probably best to ask your health visitor for advice too. That's not too bad a diet though for a 2 year old, just gradually build on it as she gets older. Will she eat a vehetarian sausage, as that is made from quorn which is an ok soursce of protein? Also you could make a puree from lentils and mix it in with the tomato sauce.
Good luck!