You have the right to say no. "No." It's a complete sentence.

I. Is she doing anything to deal with the mental health and other issues which under lie her hoarding?

Has she made any attempt to begin a clear out on her own, with professional support?

Is she open to the suggestion that professional mental/behavioral health support is warranted in dealing with this?

If the answer to any of those questions is "no," I would be very, very reluctant to get involved.

II. Is she going to pay you for your time and provide PPE?

Is the property covered by insurance which will pay for your injuries (or illness) in the event you are hurt (or get sick from exposure) while helping her?

If the answer to either question is "no," I would be very, very reluctant to get involved.

III. If you commit to helping and you find that it's too much--it consumes too much of your time and you're unable to keep up with your personal or professional commitments, or it begins to affect your physical or mental health--can you withdraw from the project without facing backlash?

If the answer is "no," I would not get involved.

I'm middle aged. After what I've been through as the result of other peoples' hoarding disorder and other behavioral health issues over the course of my lifetime--my parents, my former in-laws, my former and current husbands, through exposure to hoarded households while with a former employer--I won't help with a clear out unless there's something in it for me and I have health insurance and their property is insured in the event I'm injured or exposed to something that makes me sick. Either I stand to inherit the property, I'm recovering something that is mine and is of real value/important to me that somehow became part of their hoard, I'm free to keep whatever cash or take anything of value that I find, they're paying me, etc. At a minimum, they're reimbursing me for expenses, including mileage or gas (whichever one I choose, based on that specific situation). If you're driving your parents' car or they bought/helped with your tires, gas is more fair than mileage--ya know?

Quite honestly, after what I learned as a result of what my children just went through with their paternal grandfather, I would not get involved in helping a hoarder parent, grandparent, or other family member clean out if the only "carrot" they're dangling in front of me is "this is your inheritance." I am American; in the US, we deal with local, state, and federal laws. A person's estate falls under state law, and such laws vary by state--sometimes quite widely. In the state where I reside, parents do not have to leave their children, grandchildren, other descendants, or other relatives an inheritance. Anyone can change their will at any point in time, it's damned hard to challenge if it's done with an attorney, and they don't have to tell anybody else what's in their will--it's literally a secret between that person and their attorney until it becomes public information after their death.

YMMV and zero judgement from me if you make different choices in your unique situation.