Peña-Alarcón previously worked as an Assistant Auditor for PricewaterhouseCoopers – Service Delivery Center (1997-1998), conducting financial statement audits for banking institutions and credit unions. Afterward, she briefly joined Empresa Petrolera Chaco S.A. as an Administrative Assistant in 1998 before starting as a Corporate Loan and Trade Officer at Citi in 1999. With Citi, she analyzed financial documentation to assess the financial soundness of corporate clients within the energy and agriculture sectors. In 2002, Peña-Alarcón served as a Project Assistant for the Organization of American States, where she assisted in preparing budget and expenditure reports, coordinated administrative duties, and coordinated and recruited interns.

Peña-Alarcón joined the Pan American Health Organization in 2003 as a Project Assistant. In the role, she helped develop a manual promoting quality of life for Latin America and the Caribbean. She left in 2004 to become a Specialist and Project Coordinator with Organización de los Estados Americanos. She coordinated a $1.3 million Biodiversity Grant Program in Washington, D.C. that helped NGOs and local institutions improve decision-making through data readiness. Peña-Alarcón was promoted to Specialist, Regional Project Manager in 2008, where her responsibilities expanded to include developing the Caribbean Sustainable Energy Program, supporting government officials to establish the National Energy Policy and Action Plan in Antigua and other municipalities, and creating an energy literacy program, among other duties. From 2013 to 2016, she served as a Specialist, Project Manager working in sustainable energy for Latin American and Caribbean communities. In the role, she grew the organizations' previous work and monitored and evaluated various funds.

From 2016 to 2019, Peña-Alarcón worked as an Independent Contractor for the National Renewable Energy Laboratory, working with management at various government agencies in Latin America and the Caribbean to ensure access and availability of the Clean Energy Solutions Center program. She also led webinars and provided technical assistance to clients and officials. In 2017, she joined the Pan American Health Organization again as an Independent Contractor. Until 2019, she helped support technical cooperation to acquire medicine and strategic health supplies. Afterward, Peña-Alarcón joined USA for IOM as an Operations Liaison. With the organization, she helped raise awareness, including fundraising, for humanitarian assistance for vulnerable communities displaced by natural disasters, climate change, and conflict, as well as victims of human trafficking. Furthermore, she coordinated with philanthropies to enable funding for migrants impacted by hurricanes and the pandemic in the Bahamas, Trinidad, and Tobago. She left the organization to work with the Environmental Defense Fund in 2022 as the Project Manager of the EcoMadres Program. Peña-Alarcón currently works with the D.C. Chapter of The Climate Reality Project. She has been involved with the organization since 2018 and helps advance climate action through awareness. She is also the Founder and CEO of Terra Solutions LLC and the Sustainability Lead for The Round Group. In 2024, she co-founded Raices Collaborative, a Texas-based NGO.

One of Peña-Alarcón's most significant career highlights involved the creation of Terra Solutions LLC, a venture born out of a personal calling in late 2023. Beyond professional milestones associated with starting her own company, the organization reflects her deeply rooted commitment to sustainability and environmental justice. It is rooted in passion and aimed at creating positive change. She states that Terra Solutions embodies her resilience, learning, and sincere desire to contribute to a more sustainable and equitable future for all.