But remember, you can pull anyone from any point in their canon. Donna, before losing her memory. Amy or Rory before the Angels. Maybe even before they know she's their daughter. There would be gentle side-stepping from River anyway, until she knew they knew. Spoilers! But it's not like any companion ever got separated from the Doctor while still his companion. *snerk*
Vastra cannot take on a human appearance, which I think is in our rules. You'd have to check.