Wheelchair

I'm not sure about this, but I think she was just using the wheelchair as a tool to manipulate people (like her nephew and his wife), to make people think she needed more help or attention.

Right after she burned Edna Tinsley's belongings and was sitting at the fire, she rubbed her ankle. I assumed she injured her ankle during the killing.

It's been quite a while since I read the book but I believed it was left from when she broke her ankle a few years before.

Why was Mrs. Marrable in the wheelchair? I don't believe that was ever explained.
______________
There was no explanation. I saw the intention, as another manipulation of Marable. She could gain sympathy, by putting up a front to mask her ghastly deeds. What a frail and precious little old lady she was.