In 1984, while still attending college, Reller began her career at Great Plains Software. She joined Microsoft Corporation in 2001 as part of Microsoft's acquisition of Great Plains Software, where she had served as a chief financial officer (CFO). After serving as a corporate vice president within the Microsoft Business Solutions Group, she joined the Windows division in 2007 and in 2009 added marketing responsibilities while retaining her role as chief financial officer. In 2012, after the departure of Steven Sinofsky, she assumed responsibility for the Windows business in addition to serving as chief financial officer and chief marketing officer of the company's Windows division. In July 2013, she was promoted to executive vice president of marketing at Microsoft Corporation.