I have heard of Genworth, but I don't have any specific experience with them. One suggestion is to go to this website - National Long Term Care Ombudsman -
http://www.ltcombudsman.org/default.cfm - and see if the ombudsman in your state can help. The other suggestion is to contact your state insurance commissioner. They vary from state to state in terms of consumer help. Here in Washington state, the commissioner is historically a strong proponent of consumer rights, and insurance companies know it.
I started paying for long term care insurance earlier this year, because I'm terrified of being a burden and being alone and unable to care for myself later in life. But in comparing policies, including Genworth, it became clear to me that most companies will likely make it difficult to successfully have a claim. Much more so than regular medical insurance. Your mother is lucky to have you to be her advocate. Don't stop with their rejection. Push it.
Good luck to you, and again, your mother is lucky to have you to help her and to make sure she doesn't get ripped off.
b_b