But before she can beat anyone, Rehrmann knows she has to boost her image beyond her own turf north of Baltimore City. That's the reason for her current month-long "courtesy call" tour of the state, where she is hoping to increase name recognition in time for the serious campaigning next spring.
"That's what campaigning is all about - getting your name out and discussing the issues," said Rehrmann, a 52-year-old mother of four and grandmother of one.
Rehrmann is a former state legislator who is now in her seventh year as Harford County's highest-ranking elected official. She is barred by term limits from seeking re-election.
She is known as a pro-business social moderate who has kept tight controls on spending in her fast-growing county.
"I watch taxpayers' pocketbooks very closely. I know who hard people work for their money," Rehrmann said.
She is the only Democrat who has announced a primary challenge against Glendening. Others, such as House Speaker Casper R. Taylor Jr., D-Allegany, and U.S. Rep. Benjamin L. Cardin, D-Md., considered bids but ultimately chose not to run.
Some have said her candidacy can only hurt the party, by forcing Glendening into a primary fight when he could be saving his energy for the general election and Sauerbrey.
But Rehrmann has been undaunted by the criticism and is vowing to continue her push for the State House.
"I believe we've got a great state that can be better, and people want leadership they can count on," she said.
Beating an sitting governor in a primary election is almost always an uphill climb. Name recognition and an established statewide political network are two big factors working in Glendening's favor.
But Sauerbrey also had little statewide name recognition in 1994 and she came within 6,000 votes of beating Glendening, using a campaign message centered on a state income tax cut.
Rehrmann will likely have to come up with another platform since Glendening and the General Assembly approved a 10-percent income tax cut last spring.
One area she sees Glendening being vulnerable is education funding. The governor supported a $254 million aid package for schools in Baltimore City, despite the objections of many lawmakers and others like Rehrmann who thought the money should have been spread wider. Another battle could be looming during the upcoming legislative session over a similar funding package for Prince George's County.
Rehrmann said the state needs a comprehensive, not piecemeal, approach to funding schools that need more money.
"It's divisive. It's `Let's Make a Deal.'" And I think the issues of education are too important," she said.