Turns out she's not a big 3-month old kitty. She's a very small 6-month old kitty! So she's not going to be big, though the vet said she might still grow into her paws. The neighbour who passed her on to me said she was skin and bones when she arrived on my neighbour's doorstep. It speaks much to Tabitha's strength of character that whatever hardships she may have experienced don't seem to have at all daunted her curiosity and zest for adventure. It's a good thing I didn't know, because I wouldn't have taken her (I really wanted someone younger to make the adaptation to the dog easier). But I love her to bits, and she seems well able to cope with life with Robinson, so everyone's happy.
That makes me put out a prayer for all other lost kitties, that similar blessings may fall to them.