I think it can stand alone! It’s pretty short but I don’t think it’s too informal to be a full name.
[name_f][/name_f][name_f]Margaret[/name_f][name_f][/name_f] is the other obvious option to me. I also like [name_f]Megara[/name_f][name_f][/name_f]!
[name_f][/name_f]I think you could probably use any other [name_f]Margaret[/name_f] variation and call her [name_f]Meg[/name_f] – [name_f]Margarita[/name_f], [name_f]Margot[/name_f], [name_f]Margery[/name_f], [name_f]Margarethe[/name_f], etc.