Evening

I'm helping a distant cousin of my husband with their shared family tree. She lives abroad and has no contact with her immediate family. She was informed that her mother passed in Lincolnshire in 2017 and would like to know for her own mind what she died from; however hasn't been able to find a death record to be able to order a death certificate. I've also searched Ancestry and can't find anything

Please can someone kindly suggest how else we might be able to search for this?
Thank you!