I know a little bit about the impact shield seats. First of all, you have to take the safety claims with a pinch of salt, the manufacturers like to claim that a 5 point harness used forward facing is terribly unsafe, which just isn't true. We know that forward facing is less safe than rear facing, but although the impact shield reduces the neck loading compared to a forward facing seat, it's nowhere near as much as rear facing reduces it.
OTOH rear facing advocates have been going in the opposite direction and pointing out the flaws with impact shield seats - they have higher chances of ejection, especially in rollovers (which are more common if you drive an SUV style car) or in a frontal offset crash, which are a fairly common kind of head on crash. They are also known to have higher abdominal loads compared to a 5 point harness.
So overall, they aren't any safer than a 5 point harness seat used forward facing, but they also aren't any worse. It works out about that the extra risks cancel out any potential benefit (statistically, according to real life crashes).
What they do tend to be really good for is reducing misuse, because they are really simple to use and hard to make mistakes with. They can also be good for persistent escapees, and they tend to be quite light and fast to fit so good for people who swap cars a lot.
In terms of the three you mentioned, the Pallas S is the bog standard impact shield > high backed booster seat so all of the above applies. It has an 18kg limit on the shield, so probably won't last long enough for you.
The Pallas G is approved to the newer regulation and works slightly differently in that it has to be fastened using isofix and top tether and then you affix the shield onto the front using clips and tighten it. Because of all this, it's slightly less easy to use than the basic one and has more potential for misuse, but OTOH the newer regulation did include some guidance about ensuring that the forces from the shield are directed towards the pelvis, which might reduce some of the abdominal loading and might also ensure a tighter fit reducing the ejection potential, but this is all just speculation and guesswork because it's the only model like that on the market and that is too niche to show up in any statistics or research studies. It does have a higher weight limit of 21kg, though a height limit of 105cm for the shield.
The Anoris T has the newer regulation too, so all of those "possible" benefits, but the main thing about this one is that it has airbags inside the shield, which work the same as airbags in the front of your car and help protect and support the head and neck in an accident. It also uses a support leg instead of top tether which makes a lot more sense for this type of seat. The crash test data that has been released is superb, it's a really impressive seat, but it does have a hefty price tag, again, it's up to 21kg (but 115cm this time), it doesn't convert to booster seat and it's much too niche to have any real-world data about it, so we don't know if the ejection/abdominal loading issues are reduced. It's likely that it's safer than a normal forward facing seat, but I'm not sure it's really the safest ever, as Cybex claim.
Going back to your current seat, car seat straps should go over the shoulders either side of the neck. It would be really unusual for her shoulders to be too narrow for the straps, as the gap between them is generally only a couple of inches, if you look at where they are attached to the seat. Therefore, I think it's most likely that the headrest is set too low - this causes the straps to sort of lean out to the sides. The picture on "Step 2" here is how they usually look when you have the harness set too low. (I'm using harness/headrest interchangably, because in these seats they are joined together and adjust together.)
https://www.goodeggcarsafety.com/blog/5-steps-to-strap-your-child-into-their-car-seat-correctly.html