I suspect she's nesting in it because it's near the wheel
And because the carrot topped hide isn't quite big enough to tempt her in. You can actually get a guinea pig sized one of those carrot topped hides that makes a good large house. The only thing is it then needs replacing if it gets pee'd in whereas cardboard is cheaper.
If you have the funds, then something like this one is good. I use this for all my Syrians and they all move into it (although one of mine sleeps under it rather than in it
It has legs/stilts as well so it won't sink in the deep substrate. They do need supporting underneath as the hamsters tunnel under them sometimes and it could sink and hurt them.
Slot Together Wooden Hamster Chamber House Made from robust materials Assembled without glue or nails Flat packed to save on packaging materials Modular, allowing you to change the design to suit your requirements Chambers can be changed into two main configurations Removeable roof for checking...
www.happyhenryshomes.co.uk
You choose the length of stilts depending how deep your bedding is
www.happyhenryshomes.co.uk
If funds are tight after getting the new cage then a shoe box house is fine
I find if there is a large house, that is dark inside, and with a toilet inside, the hamster will move in and start using it. It helps to put a smelly treat inside at first (eg cucumber) and a little trail of sunflower seeds leading to it. And a pile of torn up toilet paper strips next to it. They usually move in within a night or two, having investigaged.
A good place for a large house might be on the left of the cage, with the door pointing towards the wheel (ie opposite the wheel) then maybe have the carrot cottage in the middle. A few more things to fill up the space would help too as they often don't like being too exposed getting from the house to the wheel. So more tunnels or hides in the centre part can help. Eg the carrot hide and the cardboard tunnel you have already. Also pringles tubes make good tunnels
they are just the right size for a Syrian. You just wipe out the inside and remove the metal end. I actually pull the silver paper out as well, you just pick at one corner of it and it tends to unravel and can be pulled right out in one piece usually.
A large cork log can be good for the centre part. It's a big tunnel to run through and something to climb over and an interesting texture for them.
So maybe a shoebox house and a large cork log?
This place is good for cork logs and quick delivery usually. You choose the one that you think is about the right size and shape.
The one on the top row on the right looks good to me
Cork Caves / Hides. Caves and hides are perfect for decoration, hiding and nesting. The Cork Shed UK. Full Worldwide Delivery on all cork products.
www.thecorkshed.co.uk