Well, when she gets clipped, I wouldn't go in the room, talk to her, let her see you, etc. That way she doesn't associate you with the clipping. I do bird groomings (been doing it for... 5 years now?) and, often times, they run back to the person they know like you're saving them from the 'bad people'
For her diet, I would remove sunflower seed completely, if possible. Sunflower is high in fat and recent studies have linked it to aggression, stress, and plucking - it's like birdie caffeine. Try supplementing her diet with lots of fresh goodies, but go light on the fruit - that also has been linked to higher aggression levels. Egg is great for them, rinse the shell and hard boil it, then chop it up fine (shell included) and sprinkle it on her food - it gives her a good source of protein and calcium all in one!
If you can get her eating pellets, that's fantastic, but as an older bird, she may not take to it well, it may take time and persistence. I've had a lot of success with little birds putting them on small sized, natural pellets - my guess is it looks a lot like seed!
You can try Roudybush Nibbles, Harrison's Super Fine, or Exact Naturals for Cockatiels/Parakeets. I think ZuPreem Parakeet is about the same size too!