hi there, we are going through the same process at the moment, but for our little girl...
The inquest is designed to provide answers about the cause of death, and as the family, you have the right to put forward all the questions which you would like answered. You also have the right to put forward any witness statements or other information that you think might be useful, although the coroner is not obliged to use it if it is deemed irrelevant. You also should be given a copy of every piece of information that the coroner's office has collected, or intends to collect. If you do not think this information is sufficient, you should say so.
You should have your own coroner's officer who is responsible for your mother's inquest, and you have every right to ring up the coroner's officer and ask them directly what is going on, and email them with your concerns about the delay, especially if there doesn't seem to be a good reason.
There are certainly coroner court support services available, www.coronerscourtssupportservice.org.uk/ although it appears it is not available fully across the UK. However, the website gives you an overview of the coronial process, and what you can expect, so it is still useful.
If you are really concerned about any aspect of your mother's care, then you can see if a clinical negligence laywer would be willing to take on your case on a no-win, no-fee basis. It would mean a subsequent civil case after the inquest though, which may be more than you want to deal with after all this time. However, the coroner's role is to do all they can for the person who died, so in theory this is not always necessary. Guess it depends on the circumstances.
I hope this helps. I'm sorry that you are dealing with all this.