thanks to all of you for replies!
So, a quick update.
This morning I could not resist and desided to part clean the cage as the smell was overwhelming. By the way, I noticed it's quite volatile as when I open the window (moving the hamster to another room of course) in 5-10 min it's all gone.
Coming back to the cage cleaning. The wheel and the edges of the bowl with sand were covered in a smelly (and a bit greasy maybe) stuff, so I had to soak it in very hot water for good 10-15 min, especially the wheel and then spray with special cage cleaning anti-bac spray. Now they nearly do not smell (let's hope it's enough for her to still feel it!).
The house. it took me a while to take her out of it as she resisted up to the very end and even a pumkin seed and a slice of yellow pepper did not help. Anyway, I had to insist and took her out. The amount of poo was normal (as well as shape and size), wetness from pee wasn't a lot either and located in one corner of the house. She also did not drink a lot, it's not my first hamster and as I siad i've got a diabetic one before so know what it means. And this corner of the house was the smelliest bit, very strong, I'd say nearly intolerable. Not sweet, just a smell of concentrated urine.
I took some wet pieces of beddings and put them into one corner of the cage to try to toilet train her in the future and soaked the house in the hot water. In a meanwhile she tried to bury herself in woodshavings (I put lots of them for her in the cage) or hide in an empty loo roll and that's how I took her out of the cage to inspect. She looks ok, no wet tail definitely, no obvious damage or imflammation. Just VERY scared little creature that sits still with ears completely pressed to her head and shaking. In my experience it's the first hamster that is SO scared. Eventually she became more active (linseeds helped to speed it up) and I could hold her in my hands (don't know if i did the right thing at this point or scared her even further?).
After I cleaned the house I put new beddings (I use shredded paper for Pets at Home) and brought her back to the cage. She immediately went inside and i haven't seen or heard her ever since.
To conclude. I believe this smell is the conbination of stale urine from the house and scent marks in the cage (this greasy stuff on the wheel and bowl edges), and hopefully it will decrease with time. Alternatively i will have to spot clean her cage (house) very frequently. I know it might be quite stressfull for her but I can tolerate such a strong smell up to some point only. Plus when it comes to autumn/winter, I won't be able to aerate the room that often.
I'll keep an eye on her and keep you updated if the smell persists. At this point I would have to take her to a vet (money's not a issue, rather I need to find time off work to do so).
Thanks again for your advices and comments. Let's hope my smelly little girl (well, she's not that little I must admit!) will get less stressed and therefore less smelly
