I suspect she is worried about feeling in the power of strangers and, because of her dementia, can go from thinking about a possible bad thing that
could happen to turning this into a 'memory' of something that has
actually happened. No reason not to mention it to staff though, in a tactful manner.
It sounds as if she's had nimble care workers buzzing around at speed and it has made her nervous. She is used to the rhythms and routines of home. Here, in an unfamiliar place, she is just processing what someone is doing and they've zipped off to do something else. Even putting her plate down on the table might seem to her like slapping it down if she needs to take time to work out what they are doing?
I read your post and thought I would have done exactly the same when faced with her anxiety; re-assuring her in an upbeat manner, making light of the fears, and distracting her. Then I thought of a video I had seen recently on YouTube where the dementia specialist Teepa Snow said that this might not be helpful. If someone tells you they are worried, or frightened, they don't want to be told that it's all OK, it's like saying "you shouldn't be feeling like that" or "I don't believe you".
And, if you distract without acknowledging the person's worries, it can feel like you are saying "I don't want you to tell me about your feelings, I want to do something else instead".
It made me think very hard about how I am always reassuring my mum and MIL in a bright cheery voice, as if they were small children, and perhaps I am patronising the h*** out of them?
I think that Teepa's approach would be to acknowledge the feelings expressed, then moving the person towards a positive activity or thought process.
Scenario:
Mum: Have you come to take me home?
You: You want to go home soon. I understand how you feel.
Mum: Are you taking me home now?
You: I know you are looking forward to going home at the end of your holiday. Look what the girls have done for you - they've made you a holiday calendar so you know when you are going home.
Mum: That's a long time.
You: It must feel like a long time to wait. I'm looking forward to bringing you home on [insert day/date].
Then try some distraction, such as finding out what she's been doing today. Do these lovely care workers keep a 'holiday diary' so that she has something to bring home to share with you? Perhaps, if not, you could provide a simple book that they can write in, Mum can write in, and souvenirs can be stuck in like menus and entertainments activities, craftwork, and maybe even some photographs? She could also get other residents to write things for her, like an autograph book.