I don't have all the answers, but it seems that you do have the correct Mehitable. 23 Jul 1817 (Canaan, ME) -25 Oct 1864 (Stowe, VT- buried in Waterbury, VT). I have been to the cemeteries in Maine where several of the siblings are buried and I have found no trace of her being there.
NS Colby was born in Waterbury. It seems they married and returned to his hometown. It would be the Colby family that have the dense population in VT, not Buzzells.
To the best of my knowledge, the rest of her family remained in Maine. Father, Joseph, lived his entire life in Canaan, ME and Charlotte's family comes from York, ME. This may be where the confusion lies, in terms of birthplace. Many times, births in York were recorded as NH.
The siblings, as I have them, are: Mary, Mehitable, Joseph, Elijah, Angeline, Nathaniel, and Harriet. I don't have too much information on all of these people, but I do have more in-depth information on Joseph, of whom I descend.
Ancestry, FamilySearch, and NEHGS don't have much information this line of Buzzells. Many of the recordings in rural Maine have been lost. The Buzzell family was not Catholic, so the Church doesn't have record either. Hope this was some help. It may have created more questions than answers.