Hi, Brooklyn and friends! Welcome to the forum and thank you so much for taking in two birds that needed a home!
Tiels are not big on eating fruit but they do eat veggies and love their greens. I suggest you take away the seeds in the evening and, in the am, about one hour after sunrise, give her gloop (check the diet section for recipes from easy to complicated) and a leafy green. At the beginning, you will have to make a simple one with only whole grains and mix a bit of seed into it to tempt her into trying it - but, as she starts eating the grains, you can start adding veggies (start with corn, they all love it!).
The too is going to take time... Like BW said, it does take them months and months to get used to a new home, especially when they have been not treated right and passed from one hand to another. These are birds that bond very deeply with humans and suffer more than other species when they are not treated right... They are also hormonal bird that are often kept at a human schedule and fed too much protein which makes things VERY difficult to everybody involved (mostly the poor birds themselves). Establish and religiously stick to a daily schedule and routine (it goes a long way to help them feel more at home), feed her a fresh food diet (they are EXCELLENT eaters!), give her a nice bath two or three times a week (it distracts them and they love bathing so it's still one more positive thing that you are giving her), give her A LOT of wood and hard cardboard to chew (most of them love having a box large enough so they can get inside and chew it). And, most importantly, learn to read her body language. The good thing about toos is that they are easy to read once you get used to them. I also use the calm, soft voice but only when they are overly excited (they scream and display almost non-stop) but, if they are being 'normal', I actually use what I call a 'high energy' voice and manners (I praise them profusely in a high-pitched, loud and happy voice and I dance with them (they like to bop up and down either with their heads or their entire bodies, they whip their head around hard and fast, etc. This is always done with them perching in front of me (not ON me) and with their bodies at my head level (because we are 'flock' and 'equals', you see?).