Healthy, happy, well exercised, well fed guinea pigs who live in a clean cage should not smell bad at all. Every animal has their own kind of smell. But unless you really want to find a reason to complain... the smell of a happy healthy well exercised and well fed guinea pig who lives in a cage you keep clean, and I am speaking of the smell of my guinea pig Maximus von Lichtenwalder who is a boar, his smell is delightful to us. He smells clean, soft and warm with the tones of his diet, hay, cucumbers, grass, and so on... but I am totally responsible for how he smells, and how much- if I do not spot clean his cage daily of course I am going to be responsible for the build up of urine and rodent poop which will ultimately smell in any room especially one that does not have good ventilation and is closed up all day...
I think from the experience I have had with keeping one guinea pig, it is not the way to go. These animals come from big families in nature, they are much more active and happy when they have a friend of their own kind to live with, especially if they have chosen their friend and they bond well.
It's a very big consideration you are stepping into, make sure that your Mom is totally happy before you regret things. Perhaps you can arrange a few visits to a rescue that has large c&c cages and groups of piggies living together. Let your Mom see and get the feel of how it could and should be before hand. Have you thought about volunteering at a piggie rescue...
Nothing has to happen this red hot instant, I took 9 months actively looking into things and making decisions, re-thinking those decisions and coming to new conclusions before my friend suddenly dropped my foster piggie into our laps... I would have two in a flash if she would agree to take both if and when she returned...
oh but pigs are wonderful, take your time enjoy the process...