Sarah, Thank you so much for doing the research.I'm not surprised that Anna Powers is not listed. Her daughter Anna and Anna's husband Seth died in randolph, VT and I can't find any burial site for them.It was probably a burial on the land with a wooden marker. I do have probate records for them however. Benjamin Powers was still in Twy. Island in 1850 . I guess you are right in thinking that would be where his mother was buried.
Do you need any research done here in the east or on Ancestry. I would gladly look things up for you.