88-year-old Michael Gibson died in a care home near Bicester.
Dr Cathy Gardner had served a pre-action letter on Matt Hancock earlier this month, demanding he retract his claim that he placed a "protective ring" around care homes, giving him 14 days to reply.
She says that after failing to receive an adequate response, legal action for judicial review has begun against the health secretary, NHS England and Public Health England.
Dr Gardner said: "The defendants have failed to engage with my concerns, failed to disclose relevant documents and have sought to hide behind procedural objections.
"This is a shameful reply when thousands of very vulnerable people have lost their lives as well as members of staff."
Dr Gardner's father Michael Gibson died on 3 April in a care home in Oxfordshire. On his death certificate it said "COVID probable".
Dr Gardner wants an acknowledgement that the treatment of care homes up to and during the pandemic was unlawful.
She also wants an admission that guidelines allowing coronavirus patients to be discharged from hospitals into care homes untested was unlawful.
Dr Gardner says her solicitors wrote to the health secretary, Public Health England and NHS England on 3 June to ask that they accept responsibility for their actions, in particular:
- The failure to take pro-active measures to protect the vulnerable residents of care homes
- The discharge of patients from hospitals, without any requirement for testing, into care homes
- The failure to provide PPE and testing
- The disruption of PPE supply lines at a critical time of need
- Dr Gardner is crowdfunding to support her case.
She said: "The defendants have now replied. There is no acknowledgement of any responsibility, nor is there any explanation as to why hospitals were advised to discharge patients into care homes without testing.
"Patients with a positive COVID test were even discharged from hospital back to care homes without consideration of the consequential risk.
"My solicitors requested documents that explain what policies were put in place to ensure a 'protective ring' was cast around care homes right from the start. No documents have been provided.
"I have therefore instructed my solicitors to proceed with the litigation. I am bringing this case now so that the plight of residents and staff at care homes is not allowed to be given low priority again."
Dr Gardner's solicitor Paul Conrathe said: "It is surprising and disappointing that the secretary of state, NHS England and Public Health England have failed to provide any explanation as to why they advised hospitals to discharge patients to care homes without testing for COVID.
"We simply have no answers as to why this advice was given, and especially at a time when PPE was scarce and community testing virtually non-existent.
"The state is under a legal duty to protect the lives of its citizens, and especially the most vulnerable.
"We will now proceed with litigation that seeks a ruling from the High Court that the advice given and approach adopted was unlawful and violated the human rights of Dr Gardner and the many people who lost their lives."
The Department of Health has been contacted for a response following the latest development.
At the beginning of June, the Department of Health told Sky News they had received Dr Gardner's letter but could not comment further.
Responding to Dr Gardner's concerns in May, a Department of Health spokesperson said: "This virus can sadly have a devastating effect on some of our most vulnerable people and our deepest sympathies go out to the families who have lost relatives.
"The government is working around the clock to make sure care homes and our frontline social care workforce are getting the support they need to protect residents and tackle coronavirus.
"We have put in place a policy to ensure all people are tested when being discharged from hospitals into care homes and we have allocated £1.3bn of additional funding to enhance the NHS discharge process, as well as a new £600m infection control fund for care homes to tackle the spread of COVID-19.
"As a result of all this - and the work of so many people - two thirds of England's care homes have had no outbreak at all."