@mummy2017 - Ruth's TARDIS. Much more like the first one we saw than any from the new era.
There are lots of conflicting clues about where Ruth's Doctor fits in in if it's going to be consistent with existing canon (which is a big if!)
WhenTom Baker's Doctor was brain-wrestling with the renegade Time Lord Morbius, several faces were shown which were apparently previous incarnations of the Doctor and/or Morbius (actually they were various members of the production team.) If they really were previous incarnations then Ruth could have been one of those.
But Ruth must have come after William Hartnell's Doctor, because her TARDIS is a police box, and the TARDIS wasn't a police box before it landed in London in 1963 (we know this because in the second episode, after it lands in the Stone Age, the Doctor is surprised it's still a police box)
The implication is that she was before Patrick Troughton's Doctor, because she didn't recognise the sonic screwdriver, which was introduced in the story 'Web of Fear'. But she couldn't have come between WH & PT because we saw that regeneration on-screen.
In fact the only regeneration that wasn't shown on screen was the one between Patrick Troughton and John Pertwee, which was possibly not a regular regeneration, but just a change of appearance, imposed by the Time Lords (though there was a distinct personality change too)
There is actually a body of fiction, some of it from officially licensed sources (known as Season 6b) which explores the idea that the 'Second' Doctor was actually forced to work as an investigator and roaming trouble-shooter by theTime Lords along with companion Jamie for some time before he was finally exiled to Earth as JP's Doctor. It's possible that he had more than one incarnation during this time, though it doesn't explain Ruth asking what the sonic was. However, the sonic during Patrick Troughton's time was a much simpler instrument, resembling a pen and with far fewer functions - more Swiss Army Knife than portable computer, so she might just not have realised what it was.
Of course, there is always the possibility of alternate universes/timelines - apparently Chris Chibnall has said this isn't so, but considering the amount of misdirection and terminological inexactitude that the Dr Who production team has been responsible for in the past, one could be forgiven for taking that with a pinch of salt!