Will a vote by the Board members be sufficient to remove her from the Board?
It should be, but you should consult your bylaws to see what they say in regards to this.
Before you go ahead with that vote I would sit her down with the rest of the board and in the best manner possible tell her what the problem is and let her know that the principal is now considering disolving the PTO becuase her actions
are affecing your purpose of functioning within the school. Inform her that the rest of the board will not allow that to happen and that she needs to straighten up or you will have no other recourse other then to remove her from her board position.
Now at this point she may decide to just say screw you and resign herr seat, thus saving you from the vote. If she decides she is going to attempt to behave I would let her know that the minute she steps out of line that the board will immediately vote her out of office.
You could even see if the Principal is willing to attend this meeting with your board.
Good Luck!