That depends on your state law. Do you have power of attorney? Then you are ok. Just sign.
You may need to go to the surrogates court and have yourself declared her guardian or personal administrator. Is this a temporary thing (accident, illness) or a permanent thing (dementia, disability)? How do you plan to handle other matters that require 2 signature.
As a practical matter, the IRS won't know that an e-filed return was not agreed to by both spouses. If you filed jointly last year, you have the same AGI so you would just enter it twice. You might get into trouble only if someone else with an interest in your spouse's care (other next of kin) accused you of doing something improper.
But its always better to do things correctly. If you need to be appointed as guardian for an incapacitated person, you could check your state web site, or go to the county court house and ask the clerk to show you the right forms.
