Bad Wolf immerses herself in the swirling vortex of time. She sees it all, countless trillions of lifetimes, some broken, some intertwining. She sees the Doctor, his disjointed lifeline spilling out across all of time and... and another, a fainter lifeline, one that broke, one that hurt her with its breaking. She pulls it together simply because she can, rooting it steady throughout all time. She ends it carefully, on an abandoned city above a thriving freeway.
The vortex changes, the knock on effect of her actions becoming readily apparent. She could change it, she could go back and undo what she's done, but this... this future, this timeline is better. She can see that one tiny change to that, now almost unending, lifeline could have a knock on effect that would save billions across all time and the Universe. One tiny change and new lifelines, all connect to the first, spring up all over. There is Grace, who saves the life of her next door neighbour (he is later part of the team that discovers the cure for Alzheimers); William, who takes on an armed robber, a well placed shot leaves him paralysed, but his intervention ensures the safety of eight people who were originally intended to die; Connor, a soldier who sacrifices himself to save the rest of his platoon; Helen, quiet and bookish, who on her way home interrupts an act of violence against a young woman (she was supposed to have died, the first victim of a vicious serial killer); Steven, who dies to save the world. So many generations spawned from one lifeline, the majority of whom all contribute to a better world. Bad Wolf sees it all and watches the knock-on effect, utterly enthralled, as time changes before her.
She can feel the ache, from that fixed lifeline, a pain that grows in it's intensity. She gives the fixed lifeline companions, lovers, partners but the broken cry, the pain of the fixed lifeline doesn't end. She can see now the loves that hurt the most when they die, the true loves that were all too brief. She takes each one of those lifelines and stretches them, anchoring them to the fixed lifeline watching for the repercussions. Only one lifeline yields a satisfactory result; she takes it and anchors it permanently. This lifeline is not for forever, just till old age claims its victim.
Quiet voices in her head tell her she shouldn't have done this, but she ignores them. Beneath the exterior Bad Wolf is a young woman, one who believes in love and hope. Logically she should have left the universe and it's timelines well alone, just admired the beauty of time and life. The pained ache of the fixed lifeline lessens, if only a tiny amount as the lifelines shift. It's enough. Bad Wolf admires her work and then proceeds with her main task.
Decades earlier Ianto Jones suddenly inhales sharply and fights his way out of a body bag.