Well, my issue is, once again food. It's hard to give her treats when she refuses to eat almost everything. I tried introducing her to peas, and she just squeezed the peas, liked the juice, and moved on. She picks up strawberries, bananas, peas, etc and then walks away :/
She's still a young bird and not TOO set in her ways, but unfortunately if the breeder didn't expose her to vegetables and nutritious fresh foods right after weaning, then it'll be a bit more of a challenge. Keep trying with a wider variety of fruits and veggies (veggies in general have more nutrition than fruit). Lightly cooked, raw, cut tiny, cut small, cut chunky... Observe if she prefers it any way over another.
In the mean time I hope she is eating or will accept a good quality pelleted staple food (Harrison's and Rousybush are ones I've had good results with). I might have gotten lucky, but all my birds as well as past birds have loved their pellets and took to them immediately. Getting them on this healthy base diet is essential in case you just end up with an extra stubborn eater, who won't really touch much besides a very limited amount of fresh food.
Again, she is still a very YOUNG bird, which is good news, as they may be easier to convert than an older bird who has eaten the same thing for many years.
Keep in mind though, if she's picky and stubborn, it may take many days, weeks, months before you see her even take a small bite out of any of it. You will really feel like you are wasting a lot of money and vegetables/fruits... So, a good idea is to eat the rest instead of wasting it! This makes humans eat healthier too.

LOL, when I say eat the rest of it, I mean the extra that you didn't already cut up. The part that would otherwise go to waste. Not the part you already cut up and put into the bird's bowl! Bird leftovers haha :52: I would never suggest that LOL.
Also, you mentioned about giving treats. If birds aren't comfortable and trusting enough, they won't take a treat from your hand. BUT, Pippa does look like she's past that stage. Could be just that she doesn't have a wide enough palate yet - she hasn't discovered enough foods that she likes, or is unfamiliar with the look of the treat and doesn't see it as food.
One thing many people do, is pretend you are eating the food yourself and enjoying it. The idea is birds as flock animals will follow the 'monkey see monkey do'. However, this is not fool proof, it does not work on every bird.
If you are trying to use treats for training, of course it's nice and convenient for us to use, and really gets the reinforcement across, but you might have to just use profuse praise instead as a reward if she refuses to take treats.
Good luck!