Does Queen Elizabeth need to wear a mask when she goes out?

The queen wears a mask yes 

She issued a decree, you people are the disease, she’s the cure.

No, as Royalty she does not have to wear a mask besides the fact that her Royal mouth and nasal passages are Royal as well and no virus would dare tread upon her Majesty‘s Royal air passages.

Of course!  She isn't immune to viruses.  Nor are the people around her.

We don't wear masks because it is the law, we do because it is a good idea, and keeps people safe(r).

The Queen, as a head of state, is exempt from certain laws. For example, I as a private citizen could not start civil proceedings against the Queen on any matter.

However, the Queen endeavours to stay within the law. She sees it as her duty to lead by good example.

The Queen has observed all laws, regulations and guidelines issued in England (where she is currently residing) and so she wears a face mask when they are prescribed, she observes social distancing and has stayed in a bubble with, until now the Prince Philip, and a smaller than normal number of staff.

The Queen still needs to follow the laws eventhough she is the law.

She sets an example to others. She may be above the law, but this is common sense and a courtesy to others who are not immune. In case you hadn't appreciated it, mask wearing is to avoid infecting others, not to protect oneself.

Because the laws of masks in open air public are stupid and she knows it, just as all intelligent people simply use the common anti-virals like regeneron and especially Ivermectin (the very old and proven, most common 100% effective anti-viral) can be taken any time to cure a simply flu virus.  The numbers keep shifting of the real deaths, and included motorbike deaths, sucide, old age (90 yrs old !) and every common standard flue (average of 30k yr in USA), as if they were covid. - so the whole mask thing is a big fake to destroy freedoms of all free Christian nations.

In theory she is above the law as all laws are written in her name.

But the Queen being a very intelligent person does wear a mask when out to help protect her against the virus.

No, the cornavirus doesen´t exist.