I think you’re cage looks fine
. But needs a new wheel. The one the cage comes with is too small for a Syrian. So yes you need a 28cm wheel at that end. The other thing that keeps them happy is a large ish house/nesting box - they need somewhere dark to nest and are happy as Larry with a house big enough to build a big cosy nest in, that’s nice and dark inside (not easy sleeping during the day unless the house is dark inside. There are few good ones you can buy or you can make a shoebox house. Just cut the base out of the shoebox, so the house is open underneath and sat on the substrate (they like to bury hoards under their nest and it keeps the house aired). But a hole for a door - ideally at one end of one of the long sides (the other end is then darker). Keep the lid as a lift off roof - so you can check inside occasionally without the nest collapsing).
If you put that bendy bridge over the door it’ll make her really happy - not only does it make it even darker inside but it makes a tempting tunnel entrance to the house (plus a ramp onto the flat roof.
When I had that cage (v similar cage - identical except for bar spacing). I actually just used a large flat roofed house instead of a shelf. The flat roof doubled up as a shelf. Then I had a small shelf (lava ledge) over it.
Something like this is ideal. Not cheap but has a granite slab over part of it. A good place to put a food bowl so it keeps their nails short every time they go to eat. Also a cool pls e to sit on on hot weather. Alternatively you can have a water bottle over the granite area - soaks up the drips. And still roughens nails when they go for a drink.
It fits well in the HH along one end. Shoebox house is cheaper though!
Rodipet® +GRANiT House DALANi for Pet Rodents
For a 28cm wheel this trixie one is popular, quite quiet and cheap. She will love a wheel that size. The small ones can give them back ache or lead to long term back problems. Or they just don’t use it because it’s uncomfortable.
I’d sort the wheel first as a priority. Then she can burn off some energy.
https://www.amazon.co.uk/Trixie-6101...ixie+28&sr=8-1