Peña moved out after a bad disagreement with her mother, staying with friends and renting a room during her last few months at John F. Kennedy High School.

[3] She later attended Buffalo State College, paying her way through school with a series of retail jobs and by volunteering at a shelter for battered women[3] before graduating with a B.S.

[4] After law school, Peña started her legal career in the public defender's office in Philadelphia before moving to Washington, D.C., to join her then-fiance Markian Melnyk after failing the bar exam.

She continued to be active in public life, joining the board of CASA de Maryland and winning a seat on the College Park City Council in 2003.

[2] During the primary, she received endorsements from Democracy for America,[13] EMILY's List,[14] Sierra Club,[15] the Congressional Progressive Caucus,[16] and Latino Victory Fund.

[3][20] Peña-Melnyk supports codifying the right to abortion into the Maryland Constitution,[21] and criticized a statement from Governor Larry Hogan in 2018 that downplayed needing to do so, calling it "insufficient".

[22] Following the U.S. Supreme Court's decision in Dobbs v. Jackson Women's Health Organization, which overturned Roe v. Wade and Planned Parenthood v. Casey, Peña-Melnyk said that she was gearing up to codify abortion rights in the state constitution.

[23] During the 2022 legislative session, Peña-Melnyk introduced the Healthy Babies Equity Act, a bill that would provide prenatal care to individuals regardless of immigration status.

[26] During the 2019 legislative session, Peña-Melnyk introduced a bill that would require Marylanders without health insurance to pay a state penalty that would go toward purchasing coverage.

[28] During the 2020 legislative session, Peña-Melnyk introduced a bill that would require health care professionals treating patients in perinatal units to receive implicit bias training at least once every two years.

[35] During the 2022 legislative session, Peña-Melnyk introduced a bill to allow tenants to petition courts to shield records in eviction cases where the failure to pay rent was due to an income loss caused by the COVID-19 pandemic.