She worked to create a private student loan program for Navy Federal under Aaron Aggerwal, who got his MBA while working as a business analyst at Sallie Mae from 2004 to 2010.

The student loan program was launched in April 2015, providing an additional tool for members cover education costs while in school, or refinance school debts after graduation.

By year's end, Navy Federal held $47.4 million in student loans representing less than one tenth of 1% of its entire portfolio.

But then a ripple from Navy Federal of Vienna, Va. ($90.6 billion in assets, 7.5 million members) is a wave in the credit union movement. As the nation's largest credit union, its student loan portfolio quickly went from 17th largest in December 2015 to the nation's largest a year later with $147.8 million on the books.

Navy Federal ended 2017 with $345.3 million in private student loans.

Meanwhile, Aggerwal was promoted to assistant vice president for credit card lending in 2016, and last year Sepulveda was promoted to manager of education lending. And, by the way, she has paid off her student loans.

"Once you look at the whole student loan market, you realize what a huge piece of debt this is for the American people. Of course, our membership reflects that," Sepulveda said.

Navy Federal originated $205 million in student loans, up from $107 million in 2016. Consolidations represented about half of 2016's loans, and $120 million of last year's loans. This year, Sepulveda expects originations will continue at the numerical scale of 2017, or about $200 million.

Pentagon Federal Credit Union of Tysons, Va. ($22.9 billion in assets1.6 million members) has had private student loans on its books since 2011, and in February 2017 launched a new program for education loan refinancings.

PenFed ended 2017 with $110.5 million in private student loans, up 349.2% from a year earlier. It ranked No. 4 in private student loans at the end of 2017, up from No. 11 in 2016.

Ricardo Chamorro, PenFed's senior vice president for consumer lending, deposits and corporate development, said PenFed had more than $100 million in originations last year, and expects about $200 million this year.

Beyond 2018, he expects growth will be at the rate of the overall U.S. market for private student loans. MeasureOne of San Francisco estimated that private student loan originations rose 4.7% to $8.1 billion for the academic year that ended June 30, 2017.

PenFed doesn't have a goal or limit for its student loans as a percentage of total loans. Despite the size of last year's increase, private student loans still accounted for only 0.57% of total loans on Dec. 31.

"It's a small fraction obviously," Chamorro said. "We're trying to scale it up to something our members will appreciate. We're still learning where the market is, and what our members are demanding."

Navy Federal and PenFed together accounted for half the $571.4 million increase in the movement's private student loan portfolio last year. Other credit unions increased their portfolios 7.9% last year. If they do so again, the nation's credit unions would be holding close to $5 billion in private student loans by the end of this year.

Harvard Employees Credit Union of Cambridge, Mass. ($635.1 million in assets, 48,899 members) was among the first credit unions to begin offering student loans in 2011.

In 2011, only 510 of the nation's 7,240 federally insured credit unions had student loans in their portfolios. The balances at the end of that year were just under $1.5 billion, or 0.3% of total loans.

Harvard had $37.6 million by the end of 2011, representing 15% of its total loan portfolio. As of Dec. 31, 2017, student loans were $98.9 million, up 10.5% from a year earlier and accounting for 18% of total loans.

Thomas G. Murphy, Harvard University Employees CU's senior vice president for student and alumni services and consumer lending, said the credit union's six years of experience with strong loan performance has allowed it to serve members with more flexibility.

"We were a lot more conservative when we first launched the program," he said.

A relatively small number of Harvard students have private loans through the credit union. Harvard has about 18,000 to 20,000 students per academic year, and the credit union issues about 1,000 student loans each year.

Originations were about $18 million last year. Some are made to undergraduates, or are refinances, but most of the loans go to graduate students, whose diplomas leave them with average school debts of $33,000 to $40,000.

In the past five years, private student loans at credit unions have more than doubled, reaching nearly $4.4 billion as of Dec. 31. Last year, the portfolio rose 14.2%, compared with overall loan growth of 10.1%.

As a percentage of credit unions' total loans, student loans remain small. At the end of last year, they accounted for just 0.32% of total loans, up from 0.2% in 2012 and up 2 basis points from 2016.

About four in 10 members in December belonged to one of the 718 credit unions that offered private student loans.

During the year, 46 credit unions began offering student loans, adding $27.8 million to the movement's portfolio. Another 18 credit unions abandoned student lending, removing $24 million from the balance sheet.

New York Federal Reserve Bank's Household Debt and Credit Report released earlier this month showed Americans owed $1.38 trillion in student loans—public and private—at the end of 2017, up 5.2% from a year ago.

Student debt ended the year accounting for 10.5% of the average household's debt burden, down only slightly from an all-time high of 10.6% at the beginning of 2017. Student debt reached 5% at the end of 2008, during the depth of the Great Recession, and reached 10% at the beginning of 2015.

Navy Federal's student loans have some attributes common to other credit union private loan programs. Rates are typically lower than federal loans, and it charges no origination fees.

Also, Navy Federal took special care to ensure that the servicing component is handled by an outside company with years of experience, New York-based LendKey Technologies, Inc. Navy Federal crafted its service agreements so that members would get the kind of treatment they expected from Navy Federal. For example, LendKey has a team that only handles Navy Federal members.

Navy Federal's loans have interest rates as low as 4.09% with variable rates and 5.58% with fixed rates. Undergraduate students can borrow $2,000 to $120,000 per year, and graduate students can borrow up to $160,000 per year. Students can pay either interest only or a flat $25 per month.

"Our goal is to do right by our members," Sepulveda said. "So if they're going to need to borrow, we don't want them to not have a good credit union, Navy Federal option. If they need a financial service, we should be able to provide that for them."

"While it would be great if we could find another way to fund education," she said, "that's a completely different policy question."