Final answer:
The nurse should prioritize providing immediate medical attention to the 6-year-old girl with severe birth defects who has sustained a broken arm from falling from her wheelchair. The nurse should also conduct a comprehensive evaluation to address the girl's other health needs and concerns.
Step-by-step explanation:
The most important intervention for the nurse to implement in this scenario is to ensure the safety and well-being of the 6-year-old girl with severe birth defects and mental disabilities who has sustained a broken arm as a result of falling from her wheelchair. The nurse should prioritize providing immediate medical attention to the girl's broken arm by immobilizing it and assessing for any signs of further injury. Additionally, the nurse should conduct a comprehensive evaluation to ensure that the girl's other health needs are addressed, such as assessing for any pain, managing her medical conditions, and addressing any potential neglect or abuse concerns.