Frances Haugen, who gathered internal documents showing how Facebook Inc.’s -4.89% Instagram app FB caused depression and anxiety in many teenage girls, will appear before a Senate panel Tuesday seeking to toughen the law protecting children online. .

The Instagram disclosures, along with other documents Ms. Haugen gathered while working at Facebook, formed the basis of The Wall Street Journal’s Facebook Archives series.

Ms. Haugen “has encouraged and emboldened the effort to protect children and hold Facebook accountable,” Senator Richard Blumenthal (D., Connecticut), chair of the Senate Subcommittee on Consumer Protection, said Monday. The hearing will be a “watershed day in the fight against Facebook’s destructive damage and concealment,” he said.

Facebook has questioned the characterization of the documents in the Journal and by Mr. Blumenthal and other members of his committee, who questioned Facebook executive Antigone Davis about the documents last week.

“It is not accurate that a leaked internal investigation shows that Instagram is ‘toxic’ to teenage girls,” Facebook said in its statement. “The research really showed that many teens we heard from feel that using Instagram helps them when they are struggling with the kinds of tough times and problems that teens have always faced.”

The Journal has defended the series, saying Facebook has not identified any factual errors.

Ms. Haugen, who resigned from Facebook in April, was a product manager hired to help protect against election interference on Facebook. She said she acted because she was frustrated by what she saw as Facebook’s lack of openness about the platforms’ potential for harm and its unwillingness to address their failures.

Ms. Haugen has sought federal whistleblower protection at the Securities and Exchange Commission. She is also interested in cooperating with state attorneys general and European regulators.

The Instagram disclosures have gathered momentum to update the Children’s Online Privacy Protection Act, a 1998 law that governs websites that collect data about children. The law, known as Coppa, has been widely criticized for being inappropriate in the age of social media.

“Updating the Coppa will be essential,” Senator Maria Cantwell (D., Washington), who chairs the powerful Commerce Committee, said at last week’s hearing.

Critics say the law as drafted has measures that create enforcement challenges for the Federal Trade Commission.

One is its requirement that a platform operator have “real knowledge” that it is collecting personal information from children before the stricter restrictions in the law take effect. The other is your age limit: Only children under the age of 13 get your strictest protections.

Both Republicans and Democrats have supported updating the law.

“I have three daughters and when I read the story in The Wall Street Journal I was shocked, but somehow it didn’t surprise me,” Senator Dan Sullivan (R., Alaska) said at last week’s hearing. “Personally, I think we’re going to look back like 20 years from now and see the huge social mental health challenges that were created by this era… we’re going to say, ‘What the hell were we thinking? ’”