Technically, Queen Elizabeth II is the Duchess of Edinburgh. However, her title as Queen is higher than Duchess, so that is the title she uses officially. It would be interesting if she, as the current living Duchess of Edinburgh, could pass the Duchess of Edinburgh rank on to Camilla. Unless she creates a sort of “Dowager Duchess” rank for herself, creates the Prince of Wales as the Duke of Edinburgh, and Camilla the Duchess of Edinburgh, but I’m not sure if that would work. I’m not British. I know there have been dowager queens in the past (Queen Alexandra, Queen Mary, Queen Elizabeth the Queen Mum), but I’m not sure how it works when the current reigning Queen is also the Duchess of Edinburgh.
There could be many reasons as others have written. One more reason is that step dad wants your mom to himself, with no distractions like a child to care for. And she wants to please him. You can experience a very few mild side-effects (most humans do not) just as you can from any other vaccine. Most experience none. But, a very few do. No reason for alarm, if you are one of those few humans who experiences mild side effects after getting a vaccine shot. If you do experience them, those side-effects are short-lived, they are very temporary, and they have nothing to do with the Covid-19 disease. Those side effects are not in any way contagious, either.