The board was planning to pursue recovery of the money taken even though the cost of doing so "is probably more than it is worth - but it is a matter of principle".
Mr McCabe said whether police would be involved was a decision the board was yet to make, and it would depend to some extent on how successful negotiations to retrieve the money were.
He said WBS had been up front and honest by alerting all members to the problem.
"We are different in that we are not a bank but a co-operative owned by the members, who have a right to know."
WBS had become aware of the misappropriation in early April after the woman had already left the staff.
"We spent three months doing an analytical review as we wanted it to be completely thorough and then we got auditors in to do an independent review on what we had found."
Mr McCabe said the matter had been discussed by the board but any decision to involve police was likely to be made at the next board meeting in August.
In his letter to members Mr McCabe said they were being informed as "these issues normally generate speculation in the community and exaggeration is inevitable".
WBS has been in existence as a locally owned co-operative for 143 years.
Mr McCabe said the small staff were deeply saddened to have been let down "by one of our own".