Final answer:
Under the single recovery principle, Sheila can file a new lawsuit for the additional medical expenses.
Step-by-step explanation:
The correct option under the single recovery principle is Option 1: Sheila can file a new lawsuit for the additional medical expenses.
The single recovery principle states that a plaintiff can only receive one recovery for their injuries or damages.
In this case, Sheila was awarded $15,000 for future medical expenses. However, if she later realizes that her medical expenses will exceed $15,000, she can file a new lawsuit to seek compensation for the additional expenses.
This allows Sheila to seek fair compensation for the actual expenses she incurs due to the accident.