Ideally, your mother will have a revocable trust in place, so that you can assume the role of trustee when the time comes. If your mother hasn't signed a durable
power of attorney for finance and healthcare, allowing you to step in and help where necessary, now is the time to secure one. It's important to understand that her inability to handle her day-to-day affairs doesn't affect her ability to sign a revocable trust and will, or a durable power of attorney for healthcare and finance. In other words, even if she's declining physically and mentally, that doesn't mean she doesn't have the legal capacity to sign documents allowing you more control over her health and financial decisions. Your mother may forget to take certain medication, but it's likely she can still make decisions for herself. In general, the person signing these documents needs a basic understanding of what her assets are, who her family is, and whom she wants to inherit her property.
The capacity to sign a power of attorney for healthcare or finance is similar. Just because your mother needs round-the-clock nursing care, is physically disabled, or isn't always mentally lucid doesn't mean she doesn't know who her children are and whom she wants to make decisions for her. Your mother doesn't even need the capacity to sign her name on the document. An "X" at the signature line is all that's required if you follow the appropriate signature procedures. If she can't sign her full name, however, you'll likely want to sign the documents in the presence of a notary, who provides independent verification that your parent actually signed the document. Many notaries will make house calls for a slightly higher fee. Remember also to get two independent witnesses (not people who will inherit) when signing an advanced medical directive. These can be neighbors or friends. If your mother is already in a care facility, it may also be a requirement for an ombudsman from the facility to witness and sign the document.
If you're unable to persuade your mother to do this, you can go to court and get a conservatorship. Generally, you can accomplish this on an expedited basis to deal with most emergencies.