Final answer:
Marsha used a brute force attack, which entails trying each password until she found the one that works for her sister's computer.
Step-by-step explanation:
The method of code-breaking used by Marsha is commonly referred to as brute force attack. This approach involves systematically trying each password on the list until she finds the correct one that grants her access to her sister's computer. This method does not require any understanding of the encryption algorithm; it relies on sheer persistence and the hope that the number of passwords to try is not excessively large.