This is Normal if she has been off sick for more than the 28 week SSP period , Seems from what you are saying is that she has not gone back to work since the first lockdown in which case she would could be near the end of the 28 week
The grey area on this is that tesco have said they will top up the money if her company sick pay has come to a end but they have not said what will happen if your Goverment SSP sick of 28 weeks has ended , ( from what i understand )
What she should also be doing is making a claim for any Government Benefits she can if her SSP has run out
First step would be to get the Doctor to give her a fit note stating that that she is not to return to work due to her high level chance of contracting the Virus , Also to say that she is suffering from Anxiety
They are very unlikely to pension her off as she and her doctor are not saying that she will never be able to return to her job role or any work role ,
Yes they can dismiss her , But I cant see that happening at this time under the Virus situation , and if her doctor states she has Anxiety then they will take a very very long route to get to that stage since it would end up at a tribunal since anxiety is classed as a disability , and can you see what the papers and media would do to Tesco or anyone else if they did so
Before taking a Life style break , she needs to find out if she will be able to claim any Government benefits since she would be leaving the job her self ,
Me I would go down the route of Doctors fit note stating Virus and ANXIETY FIRST ,then see what they come up with ,
Hope that helps ,