Guinevere actually starts out as a servant in the Merlin TV series which is a spin from most of the stories with her. She serves and is good friends with the King's ward Morgana.
But she always seems to be able to get into the adventures of Merlin. While those who knew nothing about the King Arthur legend before watching show might of thought that it would be Merlin ending up with Gwen.
But it doesn't take terribly long until her love for Arthur is born. They kind of have to call it quits when King Uther Pendragon finds out and and causes loads of drama.
But when Uther dies, and Arthur becomes King, she soon ends up back in his arms. And she is crowned Queen, despite the political disadvantage and her "low birth" of class status.
Their marriage doesn't last for long as she soon is widowed when Arthur is mortally wounded by Mordred.
And after her husband's demise, she is crowned the ruling Queen instead of a Queen-consort of Camelot. Knowing the proper procedure for royal succession,. this decision seems really odd. But I did like Gwen, because she was so sweet and full of innocence. Also one of the few Gwen incarnations that doesn't betray Arthur for Sir Lancelot.