Welcome to iMore! First of all, let me express my deepest sympathy for your loss. I still have my Mother listed in my contacts, and she's been gone for several years. I completely understand how difficult it is for you to delete her. From what I understand about the redesign of the share sheet in iOS 13 is that it's "intelligent". It suggests contacts that are your favorites. I'm not sure if this will be the right solution, but it might be worth a shot. If you have your Mother listed as one of your favorites in your contacts, you might try removing her as a favorite. Hopefully, this will remedy your situation.
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