When Lynsi Snyder turned 35 last week, she received an unusually rich gift: most of the remaining shares in her family’s business, the cult burger chain In-N-Out.

Snyder had already inherited 50 percent of the company when she turned 30, and her 35th birthday triggered the inheritance of most of the burger chain’s remaining shares. With Forbes valuing her stake at $1.3 billion, Snyder has joined the rarified club of fewer than 300 women who are billionaires and is believed to be the youngest of them in the U.S.

Snyder may not be a familiar name, but her company’s business has legions of fans, including top chefs such as Gordon Ramsay. In-N-Out was founded in 1948 by her grandparents, Harry and Esther Snyder, who started the chain as a single drive-through hamburger stand in Baldwin Park, California. Through a series of tragic family deaths including her father’s demise at 49 from a prescription drug overdose Snyder inherited control of the business.

Keeping a low profile is part of her family’s philosophy.

“We back away from it, because we don’t want to be in the spotlight, we don’t want a bunch of attention. And we want to do what we do best, and that’s serve some good burgers to our customers,” she said.

As president of In-N-Out, Snyder has expanded the chain to six states from four. The chain’s menu has remained frozen in time, although fans point to the brand’s consistency and dedication to freshness as its appeal.

Every one of the more than 300 In-N-Out locations are owned by the Snyder family. By comparison, rival McDonald’s relies on its franchisees to operate about four out of 5 of its more than 35,000 restaurants.

“It’s about the quality, the friendliness and the cleanliness. We keep it simple,” Snyder said.