Has anyone know/ what happens in a mental health assessment?

Can someone please help with either some advice about mental health assessment ?
The reason for asking my mum had one done lately where her caremanger and the doctor she was under whilst in hospital came to do one as things are still not right and her main psychiatres would not change or do anything with the medication until a assessment was done to get a clear picture as one should have been done after she left the hospital two week into her respite care which never got done. I was not there at the assessment as I had been asked to take the dog out of the way so not to cause a distractions but when I came back I found out that it seemed that the so called assessment did not take place in a way I thought they were done like a job or carers interview/chat? It seem that it was planned what was going to be said and done without fully listening to the main picture of what has happen lately than just go on when this Doctor saw her in hospital.
Mum will say or blame it on something easy like the mess in the house than the real reason why she is not 100%
Anyway her caremanger and this doctor thought they would help to clean the house which is a 1st as it only been be and the OT when they could help me clean the house when rules over covid allowed them to come. They did not fully asked could this go or that could go as somethings mum said yes to were not hers to give permission to give as some were letter which had been put safe to one side for me and my dad to go through over important matters but there was items of mine like books which had only come that day and night clothes of mine put in black bags and out for the rubbish which luckily I was able to get things back than lose them. I was very upset that people with power of trust could take advantage of her. I have written a letter of complaint stating all the facts that I seem fit are correct. But wanted to make sure I had an idea of what a mental health assessment entails. Even my dad has lost his bottle over this as even though he told them to leave it he was ignored. They are due to come back but I have object to it and said they will not set foot inside the house whilst I am here as I don’t want my parents taken advantage of when I am not about . I am wondering if I should seek legal advice on the matter? Mum is still not right as some of the things that she is still coming out with make me think what on earth went on when I was not there.

This is disgraceful. They should not have done that without your involvement. How would they know what was important. It’s one thing to bin rubbish, say pizza boxes, but not personal books and papers!