Nobody goes to college hoping to become a school business official, Heather Mumby said. But after a stint in Washington, D.C., putting her political science degree to use, Mumby returned to Montana — and a job as a school business official is exactly where she ended up. For 22 years, Mumby has dealt with the ins and outs of school finance in Montana. For 19 of those years, she’s been the business manager and district clerk at Cayuse Prairie Scho…