I found this description of hostess mode (or showtime as described in this article) and actually printed it out for my mum's social worker who clearly had no idea that this was even a thing. The article comes from a publication called Coping Today, possibly American, hence the term "showtime" I hope you find it useful.
"What does “Showtime” mean?
This is probably a term that you are not familiar with but have seen it happen, especially in the early stages of Alzheimer’s or dementia, there is a surprising phenomenon that we caregivers have seen many times, and it is referred to as “Show Time.” When people with dementia are still cognitive enough to realize there is a problem, they often have the ability to put on a convincing façade of normalcy for a short period of time, say ten or 15 minutes. It is an ability that can be quite exasperating for the caregiver.
For example, you’ve been struggling with behaviors all day, especially with trying to get your loved one with dementia to get ready to see the doctor. It is always like this. He won’t acknowledge your requests or instructions. He can’t dress himself. He fiddles around while you are trying to get him to focus. It is almost as if he is deliberately trying to be late. Maybe so.
Then, you finally get in to see the doctor. You are absolutely frazzled, and you are sure that this time the doctor is finally going to understand how much your loved one has declined. But what does your loved one do? He’s smiling, bright, chatty, utterly convincing that everything is just fine. You leave the doctor’s office feeling angry and defeated. The doctor surely thinks you are the one with a problem. You’ve just experienced “Show Time!”
As long as people with dementia have the ability to “pull it together,” this behavior is understandable. They know something is wrong, and the last thing they want is for people outside the family to realize it. They are embarrassed or ashamed of their condition, so they put on a happy face. As long as it does not require logic or complex thinking, it is possible to carry on small talk and answer the doctor’s simple questions. “How do you feel?” “Fine.” “Have you been sleeping?” “Yes.” And they keep smiling.
“Show Time” can cause serious problems in families. Usually, based on living circumstances, one sibling will be in proximity to the parent with dementia and take on the task of providing care. Other siblings may be more than willing to help, but they live miles away. They may check in with you by phone, and they hear you describe all of the problems you are having.
Then the parent gets on the phone for a few minutes, and it is show time again. Your brothers and sisters can’t fathom what you are complaining about. Everything sounds fine to them. This can lead to serious disagreements about money, care practices, and family responsibilities. It’s a serious problem."