I do apologise for my original negative post! Having pondered on this, I do have a few further thoughts!
I think the rewards of being a carer depend on various things. First is the relationship you've had historically with your mum. If that's been good and you were close it will be easier (obviously) than if you were estranged or disliked each other. Next, it depends how your mum's personality changes as dementia progresses. She may remain compliant, she may not. She may become paranoid and accusatory, she may not.
But it seems to me the reason why most carers find the experience unrewarding is the nature of dementia itself, in particular empathy. As the disease progresses, the person's world closes in. Not only do they lose awareness of what's going on in the 'real' world, but they start to see only their own wants and needs, not even noticing what is happening with those around them. So it's common for a person with dementia not to notice that the person caring for them is tired, upset, unwell, sleep-deprived, angry or desperately unhappy. But it appears as though they really don't give a damn. If you're caring for a sick child or even an adult with any other illness, the reward is often the appreciation you get from them for the things you're doing. The person (for the most part) knows you are helping them, is (mostly) compliant and glad that you are there. With dementia you may get none of these things, in fact your attempts to assist may be met with hostility or contempt. Often the person really cannot see that anything is wrong with them so will resent you, perhaps because you are a reminder of what they can't do themselves.
I think it is this lack of appreciation or even just the occasional Thank You that really wears carers down.
But every person with dementia is different and who knows, it might work out with your mum. (Though I'd suggest a trial before you commit - don't burn your boats by getting rid of her home!)