After Doctor number 7 gets in the way of a stray laser shot or is bombarded by a poisonous gas cloud while trying to steer the Tardis out of a black hole, she needs to regenerate.
In this new, fan-fictiony re-imagining of Who mythos, she'd turn into Lyndsey Marshal!
Quite like Doctor 6, she's very hands on. An inventor and tinkerer, with a penchant for colourful jumpers, Doctor 8 is immensely curious and adventurous, but not without a colder, more calculating side. Sometimes it might not be wholly clear whether she sees her companions as people or components in some grand plan. This might explain why she'd have so many guests in her Tardis, none of them staying for long. Her first and most constant companion would be Pietro, an ex-monk, philosopher and aspiring alchemist.