Origin: English, Old Norse
Meaning: I couldn’t find much information on this name but the closest I could come up with is that the first part of the name, Ever, most likely comes from Old English eofor meaning “boar”, so Everina is likely an elaborate form of that.
Everina could also be a variant form of Everine, a Nordic name which also ultimately comes from an Old Norse element meaning “boar”.
Of course, in modern times, Everina could also be an elaborate form of the English word ever meaning “at all times; always”; “continuously”; “at any time”.
*Interesting fact: Mary Wallstonecraft, who wrote A Vindication of the Rights of Woman (1792) had a sister named Everina.