Question about reporting to RSPCA?

My mum came round today and was telling me about this friend of hers who has a dog. Everytime my mum has been round the house this woman always comes out and talks to her in the front garden, my mum went to her house early this morning and let herself in, the woman and kids were all still in bed, anyway my mum sais the smell as you went in the house could make you throw up, she said you couldnt see the floor of the (large) kitchen as it was covered in dog urine and faeces, the dog is completely bald on its back becuse of its fleas (obviously untreated flea problem) and its toenails are all curled up theyre that long. My mum told me that it never goes for walks but even worse doesnt even get let out into the garden (because the back door is blocked by an old washer and all other sorts of junk) presumably cos they would have to move the washer etc to let it out!! So the dog is just left to toilet all over the house, my mum was sat in the front room and the dog came over wagging its tail and she said being really friendly. I just dont know what to do, I was nearly crying when she was telling me, and i did just cry when my boyfriend came home from work,my mum was saying I cant report her cos she would have to go to court, and if they found out it was me there would be a mive fall out, ive asked my mum if she thinks she would let me have the dog, but im renting and not sure if i can have pets, also when I was telling my boyfriend he said he doesnt want a dog-I wasnt planning on getting one either!! I just dont want to ignore it its just so cruel, Ive never even seen the dog but if my landlord lets me Id love to have it, what do you think, Im in a very hard situation