It seems like the memory lapse thing with my coworker is not only continuing, but getting worse. I've made the same corrections in one of her documents three times. In one, I found a sentence that just terminated in midspan. She claimed it was always like that. I reached into my trash can, pulled out a previous copy, circled the missing rest of the paragraph, and gave it to her. She hadn't put it back into the new copy she just gave me. I found the page with the circled part in her trash can, tonight. I also sent her some copy that she claimed she hadn't received. I stood at her shoulder and told her to check her email. She went back through, found it, and said she didn't recall getting it.
Today, she told me that she accidentally mixed up some cans, and sprayed all her irises with Roundup, not fungicide like she had thought. She discovered her mistake later, and hosed them down, but doesn't know if it took---time will tell.
I hate to say this, but this pattern is looking an awful lot like signs I've seen in people's parents who were starting to have age-related mental problems. She's only 59, but that doesn't necessarily limit it.