Help for anxious cat

I am having challenges posting. Trying to make this shorter as I don’t know if my longer post got posted. I am wondering if you have advice for easing potential anxiety from my 12 year old cat who will be left alone when I am traveling for
10 days w/o her companion cat of 11years and a new to her cat sitter. My downstairs neighbor will be coming in every day and I have tried a “ meet and greet” a couple times but Olivia hid and would not come out until new person left. This is new behavior as she was always the friendlier of the two cats( her companion Sebastian died in December) I have asked my neighbor to bring a few items with her scent on them that I hope might acquaint her scent to Olivia but wonder if there are other ides anyone might have.?