[6] Heijnen attended the Geleen secondary school Graaf Huyn College and started studying law at Maastricht University in 2000.

[6] Her party won seven seats in the council, but Heijnen was not elected as candidates lower on the list had cleared the preference vote threshold.

[16] Heijnen also tried without success to bring the headquarters of the European Medicines Agency from London to South Limburg, when it had to be relocated as a result of Brexit.

She received 15,821 preference votes, 90% of which were cast in her home province of Limburg, but she was not elected due to her party winning nineteen seats.

[20] Her responsibilities included the economy, the job market, regionalization, housing, well-being, permits, social innovation, and smart city.

[21] To increase citizen participation in local politics, Heijnen organized a forum, during which inhabitants could determine on which projects €300,000 of the municipal budget would be spent, following a similar idea in Antwerp.

[25] She serves as Secretary for Infrastructure and Water Management, succeeding Steven van Weyenberg, but internationally she wears the title of Minister for the Environment.

[31] She launched a three-year campaign in 2023 to increase bicycle usage for short distances after the cabinet had the year before appropriated €780 million to improve cycling infrastructure.

[33][34] However, the European Commission warned a market analysis would have to be performed to consider alternative railway operators, and it started an infringement procedure alleging Heijnen intended to award the concession without a tender shortly before new EU competition regulations would mandate it.

[38] Heijnen went on maternity leave starting 25 May 2024, and her tasks were performed by Minister of Infrastructure and Water Management Mark Harbers.