Firstly don't worry about it looking after yourself is the most important thing at the moment.
Post Shipman things got a bit more tied up it's now for example very common now for GP's to phone the ward. Wanting to speak to the Nurse in charge of the care of someone even if expected or straight forward. when asked to counter sign a death certificate more rules on syringe drivers also got introduced.
@Drago is right from what you have said it not likely to go all the way to a formal inquest.
A PM maybe likely as it's sudden unless she had a underlaying condition and and had seen a doctor within 2 weeks up to her death.
Once results of PM are known if they show nothing to be of concern then the coroner will just "sign it off"
The only other situations that results in an automatic referral to the coroner and inquest even if due to natural causes are if they have been released from within the set time limit or held in prison, police custody, detained by a police officer at the time or detained under the Mental Health Act. Together with a few others.
Even you do get asked for a statement and they are happy with it from what you say your not likely to called to an inquest. The coroners officer will help you and support with all that anyway. Coroners court is not like a normal court yes it's formal and yes it's a court with same rules but your not on trial your a coroners witness. To help them understand what happen. In the end all they are wanting to know is the facts. What happen, when, what led up to it and can something be learned from it. On the whole MH Coroners are helpful and expect witness to be a bit worried they only really play hard ball if someone is trying to cover up, lying , talking utter rubbish or not treating them with respect.
Just focus on yourself and remember you did all you could.