Hi Lizzy,
I'm really sorry to hear your bad news. I agree with the others - strong pain killers if possible but you must decide if her life is still a happy one if you cant' eliviate the pain. I had a rottie who got bone cancer, when we found out we were devistated but spoiled her rotten for the last few months of her life, she was the happiest dog ever - lavished with love and attention and treats, she wasnt' even aware she was ill

then her illness became too much for her and she was pts, but we know we did everythign we could to make her happy.
Sorry if this is a bit depressing, i didnt know if it was the write thing to share this with you or not because I dont want to upset you more that you already are, just wanted to tell you to prioritise your dogs happiness.
all the best, katy x