"Even good kids use the word, not realizing that they're talking about people like my sister," said Rosa's brother Nick, a Maryland 14-year-old.
"We're not allowed to use the words at my house, it would be just like saying a curse word," said Nick in testimony to Maryland legislators. "We're also not allowed to use other words that are hurtful to minorities or people who are different."
Rosa -- who Nick calls the "smartest person I know" -- has Down syndrome and is now at the center of a bill in Congress to strike the term "mentally retarded" from the federal lexicon.
Last January, Nick, who is a freshman at South River High School in Edgewater, Md., convinced his state legislature to change the official phrase to "individual with an intellectual disability."
The law would affect how Americans refer to the more than 6 million adults and children who are diagnosed with intellectual disabilities.
"The word retarded is slang to call someone stupid, and we know Rosa is not stupid at all," Nick told ABCNews.com. "Words are important."
So important that Nick and his family were there Tuesday as Sen. Barbara Mikulski, D-Md., introduced a bill in the U.S. Senate.
The solution, Mikulski said, is to be called Rosa's Law, and it will cost taxpayers nothing.
"It brings us out of the dark ages and into a world of evolved sensibilities by retiring an archaic term that equates the person with the disability and substituting it with a term that references the type of disability," Mikulski told her fellow senators.
Today, the proposed federal health insurance bill from the House of Representatives still uses what many consider to be an offensive term, referring to "a hospital or a nursing facility for the mentally retarded."
And even in Maryland, the term must be used to comply with U.S. Census designations.
It all began as a family effort when Rosa's elementary school changed the coding on her education plan from "health impaired" to "mentally retarded," said her mother, Nina Marcellino.
"When I came home and told the kids, they didn't know it was the word people used to describe their sister," she told ABCNews.com.
The school principal agreed to drop the designation and Rosa's sisters Gigi, 12, and Maddie, 10, set out to get petitions signed.
The family enlisted the support of Maryland state delegate Ted Sophocleus and ultimately changed the wording in the health and education code at the state level.
Nick, a lacrosse player and a "quiet kid," became the family spokesman, his mother told ABCNews.com. "I am so proud of all my kids."
Rosa, who plays soccer and loves math and science, is particularly proud of her family's efforts.
"She doesn't really know what the law is about, but she's excited that she gets her own law," said Nick. "And we thought she should be treated equally."
At the turn of the 20th century, children like Rosa were institutionalized and the prevailing thinking was that they should not interact with so-called "normal" people.
Those who were intellectually challenged were labeled "feeble-minded" in federal statutes. But by the 1960s, that term was thrown out for "mentally retarded."