Haines became the assistant of Robin Millhouse, an important player in the South Australian conservative party the Liberal and Country League. Millhouse founded the Liberal Movement and the short-lived New LM which merged into the Australian Democrats in 1977. She was appointed to fill a casual vacancy in the Senate by the Parliament of South Australia, on the nomination of Labor premier Don Dunstan, on 14 December 1977. As a result of the 1977 Referendum the appointment was required to be from the same party as the resigning Senator, "unless there is no member of that party available to be chosen or appointed". The casual vacancy arose following the resignation of Steele Hall who had been elected as a representative of the former Liberal Movement. Controversially, Dunstan chose to nominate Haines, who had been third on the Liberal Movement ticket from which Hall had been elected in 1975. Haines was not a member of the Liberal Movement at the time of her appointment, with the party dissolving in 1976. A majority of Liberal Movement members, including Hall and second on the ticket, Michael Wilson, joined the Liberal Party, while Haines joined the Democrats.