Michelle, whose first language is Spanish, is currently learning French in college. When she goes to see her Spanish-speaking grandmother, she inserts French words into her Spanish. Michelle is experiencing:

Retroactive interference

Explanation:

Retroactive Interference (Retro - backwards) is the tendency of forgetting a previously learnt memory due to the presence of a new memory. Interference simply means the hindrance of an old memory in the unconscious human mind because of the new memory.

Michelle learning French affects her already learnt Spanish language. It forms an interference in the way of speaking to her grandmother. The acquired memory clashes with an encoded memory. Thus, she inserts french into Spanish while conversing with her grandmother.