I third the professional assistance. I've been reading on this and it has a sliver of a chance, not completely impossible, but challenging nonetheless. Vicky I'll take you up on the offer for help because this is going to be more than I can do alone.
My partner never applied for a settlement visa to the US although she did apply for a 6 month visa to visit and was refused. It didn't say because of the same sex thing but may be relevant. We figured that applying for settlement in the states would do no good since immigration is a federal issue and not up to the states to decide. I lived in California before moving to the UK and California passed its same sex 'marriage' law a month after I moved.
I agree that her assets, namely her house, will be difficult to argue the financial dependency criteria but that is set to change this year. As it stands she's in a care home for now getting rehabilitation. How long she's there depends on how well her rehab progresses but with any stroke this is uncertain. All of her doctors have advised that she can no longer live alone or without supervision, and like Vicky said, us relocating to the states is not possible with the same sex laws. If I had to move back my civil partnership would suffer and result in a dissolution which none of us want.
How dire does someone's financial circumstances have to be to qualify for financial dependency? Do I have to support her with the money I make here to meet that criteria? Wow this is challenging.
WebJ brings up another important point...do I have to have ILR to even attempt this? I've been wondering about that myself as the rules state to be settled in the UK which I don't think a FLR allows.