I don't think she controlling. The bride asked her to be the maid of honor. Claire didn't ask her. Then instead of telling her she posted a change in the MOH.
Okay, OP "offered to pay for it with no strings attached."
That clearly was a lie. Obviously OP offered to pay for it.... and expected to be consulted on every detail and be appointed maid of honor for a woman she barely knows.
At My Brother's Wedding, His Bride Told Me to Leave—So I Canceled All the Wedding Payments