I try to keep away from canned, and use mostly frozen and fresh. I usually make a huge batch and then freeze in smaller portions. I make a mix both my rats and birds can eat; parrots need a lot of vitamin A and calcium, so I make sure to add in dark leafy greens and orange veggies. More focus on veggies and grains than fruits, but they get occasional fruits. My most recent chop features a cooked grain mix, a cooked bean and lentil mix, butternut squash and seeds, green peppers, corn, green beans, carrots, peas, broccoli, cauliflower, swiss chard, cooked super green pasta, and just a dash of hemp hearts.
There will be waste, regardless, esp as she gets used to it. Instincts say if they've never seen a flock member eat it, it could be dangerous!
As far as the pellet sizes/mixes, its based on beak size, with few exceptions. For the most part of what we know about parrots they have similar needs as far as vitamins, protein,etc. There are some exceptions; we know that macaws need more fat, pionus fare better with more vitamin A, and some do better with few pellets. So the pellets are a portion of the diet, but the diet can be adjusted as needed.
As far as I know, cockatiels do best with 50% or less of their diet being pellets.