So In the Episode " The witch´s familiar" Missy told Clara about the fakt, that she has or had a daughter. A friend of mine and I were talking about various theories about her daughter and here is my version:
Missy was devastated, the Doctor had taken off without her and he was probably never coming back.
How could he? Leave his home in the middle of the biggest war it had ever faced. But then again, the Doctor could be a coward at times.
So she stood on one of the balconies of her home, their home, lost in thought.
She had not noticed her daughter, who was standing in the doorway, tears welling in her eyes "You´re going to go after him, aren´t you Mummy?" The little girl said, her fists clenched tight on either side of her body.
Missy spun round ripped from her thoughts by one of her most precious things in this world. She crouched down in front of the little girl. With her thumb she wiped the tears from her daughter´s rosy cheeks.
"My darling, my sweetheart, I could never leave you!" She hugged the little girl tight.
"You should though" Missy heard the child say as she snuggled against her shoulder.
The girl broke their hug. "You should go Mummy, you love him I know that. Also he tends to be an idiot. He´ll loose track of time or his way and he´ll never come back. But we need him. Gallifrey needs him." She smiled at her mother and then started rummaging through her pockets. When she found what she had been looking for, the little girl proudly presented it to Missy.
"Take it with you! It´s no use here" She dropped a cameo brooch into her mum´s hand.
Missy started shaking her head "I can´t little one, it´s yours! The Doctor gave it to your for your birthday, you should keep it."
The tiny Timelady shook her head as well now "Nuhuh! It´s going to have a lot more meaning if it is the thing that helps you get the Doctor back here! Also I want you to have something to remember me by" Tears started falling again, on both sides this time.
"I will be back, I promise!" Missy said, kissing her daughters hair. "I know you will Mummy, just don´t be too long."
Missy sighed; it had been so long since the time war, so long since she last strode the red grass fields with her daughter and Gallifey had been hidden or better to say lost for so long. Remembering hurt. But every night she dreamed of the war and her daughter, how she took of without her.
She wondered if her little girl had grown up to be a beautiful young woman, or if she had died because her mother was not capable of finding the Doctor in time. Not knowing hurt too. And it was the one thing that made her mad, that had made her loose her mind over time.
She was so close, the only thing stopping her from taking the Doctor away with her and back home, was dangling in front of her, unconscious and limb. This little human called Clara was the only thing standing in her way but the Doctor would never leave her like she had left her daughter. He was not selfish enough.
What do you think? Any other theories? I´d love to hear them ;)