It's annoying when pet shops sell you a cage that's too small! They do need a lot of space and a larger cage with a continuous floor area of 70cm by 40cm minimum used to be recommended by the RSPCA - many people go larger. You can have cages like yours as an add-on to a main cage, but two smaller connected cages doesn't give the same kind of normal behaviours as one larger cage.
Having said that, you have them nicely set up with lots of things to do.
Those type of cages are limited in how deep the substrate can go and they do like digging in substrate so as deep as you can go with it.
Moving things around and cleaning that often could cause quite a bit of stress though. Especially for a hamster who is just settling in. Again it is one of the downsides of that kind of cage that you need to clean it like that. With something larger and good access and deep substrate you can just spot clean mainly and only need to do a main clean about every two months. With the deeper substrate, the bottom half tends to stay dry.
Hamsters like to scent mark to find their way around as they don't see well, so if you clean everything every few days it's removing their natural scent every time and making it feel less like home and a bit strange!
I'd suggest maybe making a bin cage to add on to the current set up - or add one of the units to the bin cage. If you don't mind a bit of diy. It means cutting a hole in the front and top of a large plastic bin (eg the 78cm Ikea Samla bin is a good size) and then meshing them.
This kind of thing
https://www.google.co.uk/search?q=ik...MlA-8Q_AUIBigB
They have plenty of space to move around quickly, dig and do other hamstery things in a cage like that. One of your units added on would add a fun element and somewhere else to go.
Are you in the Uk or US? If in the Uk, Zooplus sells good cages that aren't too expensive. If you're in the US a lot of people use glass tanks to give the floor area and buy a lid for them. A 30 or 40 gallon tank usually.
Another option with just a little bit of diy and is cheaper than a lot of cages, is an Ikea detolf hack - it's a glass cabinet you tip on it's back and leave the door off then make a lid with some mesh and wood pieces. It makes an amazing hamster habitat and there's room to section off a whole section as a digging area. If you have the wall space! It costs about £40.
https://www.google.co.uk/search?q=ik...hamster+detolf
The key word is "enrichment". That includes depth of substrate for digging (they can even dig networks of tunnels if they have it deep enough!), space to roam and forage in and little hidey places and tubes inside the cage. A shelf to sit under or on and a house/nesting box to build a good sized nest in.
I don't know how long it is since you bought the second unit, but some people have managed to get a refund, even after a cage has been used, to go towards something else.
I did the same thing - started out with a 3 tier rotostak thing and found out more later (I googled hamster cage when our Syrian started getting stuck in the tubes!) and upgraded him to an 80cm by 50cm cage which he loved.
They are also better with less height really as they have a tendency to fall and injure themselves, especially the smaller dwarf hamsters, although it looks like you have it set up quite carefully for that. So a longer lower cage is better for them really. For now you could put more substrate in the base and maybe put a cardboard egg box or something similar for her to chew on.
It's great that you have come on here wanting to know more about what is good for hamsters! I learned loads on here.