Maryanne Merriwether was given "phenomenal cosmic powers" in 1943. The exact nature of the accident that gave her her powers has never been revealed publically. Maryanne was married to Great Brittain's genius inventor Elias Merriwether. Dr. Merriwether was attempting to create a weapon to end the war. His graviton bomb experiment went badly and the resulting explosion killed him and demolished his estate. His wife was transformed into a being of cosmic energy, their young son Elias, Jr. was with Maryanne's parents. Maryanne became Britannia and fought the nazi's for the rest of the war.
Her life after WWII was one of public service, she was forced to leave much of the raising of her son to her parents as she fought crime, natural disasters, and generally lived the life of a public hero. She was on the original New Knights of the Round Table team, worked with UNTIL in its infancy, and grew more and more miserable. Finally, in 1956 she could take it no more, her son was a teenager and she had barely known his childhood. Giving over the title of Britannia to a younger woman, she retired.
Her son barely acknowledged her and she became increasingly distant from much of the world. One day, she decided to leave Earth to see the wonders of the universe. She didn't get very far. Longing for home always brought her back after a few months. She and Elias reconciled their differences in 1982, and she returned to a life of a hero in the early 1990's, taking the name Silver (in reference to her appearance when her force field is up). As her friends have passed away and her son has aged to his sixties, Silver has found it increasingly less comfortable for her to remain in the UK. She has relocated to San Fransisco (a place she and her husband had vacationed in her youth) and joined up with the super team there.
Silver fights crime out of a sense of duty and, well, boredom. She is trying to lose herself in her job to enable her to forget the life she once had. She keeps in contact with her son by email and phone and flies to see him on his birthday, but she is very uncomfortable with his mortality. She enjoys the company of long lived individuals when she can find it (Nilrem, Atlas are good friends).
"In my day, men new how to treat a lady. I used to beat them up too."
Failry standard Cosmic power house. She tends to hold back on her blasts and punches until she is sure that she won't do permanant damage to her target.
If she's too tough for your campaign lower her attacks and defenses until they are more in line with your campaign limits. If she's too weak, give her more variety of abilities, it's far from inconcievable that she would have a more varied repetoire by now.
An attractive woman seemingly made of silver with glowing violet eyes. When her forcefield is off she retains her metallic silver hair and violet eyes (though the eyes don't glow) and a youthful and beautiful face. She tends towards more modest fashions.