Neither my husband or I speak to his mother, who I understand has a lot of health problems these days. Like you, I can't bring myself to feel any real pity for her. She used to make up / exaggerate illnesses for attention and now she's got what she wished for.
I think you are taking the right approach in giving your support to your husband as he is bound to be affected by this. We're still close to my husbands sister and I do sometimes ask how her mum is because I know it can put a strain on her. I honestly wouldn't care if the woman died tomorrow but I'd be very upset at how it would affect my sister in law and our niece and would do everything I could for them.
So no, you're not alone in feeling like this. Keep a polite distance, and be there for your husband.