I'm sorry about your mother, but there is no option to expedite your case until after your Priority Date (PD) becomes current. No lawyer anywhere and no amount of additional documentation can help to expedite your case now, regardless of your mother's condition. The only option for you, as far as your F4 case is concerned, is to wait for your PD to become current, maybe in around 4 years or so. Alternatively, you may try applying for a B2 visa to visit your mother.
Refer to https://travel.state.gov/content/travel/en/us-visas/immigrate/national-visa-center/immigrant-visas-processing-general-faqs.html#ivp7 --
I have been waiting for a very long time for my relative to get an immigrant visa. Now there is a family emergency and I need my relative to immigrate soon to the U.S. Can NVC help me?
If a visa is not available, unfortunately there is nothing that NVC can do to expedite the petition. Immigrant visa processing is governed by the Immigration and Nationality Act of 1952, as amended, which controls availability of visas. There is no provision within the law that would allow the Department of State to issue a visa to someone for whom a visa is unavailable.