When Nana has trouble remembering Spanish words due to her learning a French vocabulary she learned the previous semester, she is suffering from proactive interference.
It occurs when an individual is influenced by old memories, disrupting the development and fixation of new memories.
Therefore, this phenomenon occurs when there is an interference of old learning in relation to new learning.
So, the correct answer is:
Find out more about proactive interference here:
https://brainly.com/question/9311250