Mariah developed a fear of the water when she fell off a river raft last summer. this year, she took swimming lessons and thought she had finally overcome her fear of water. she was eagerly looking forward to an upcoming rafting trip, but as soon as she stepped onto the raft, she was instantly terrified again. this illustrates the classical conditioning process known as?

Baesd one the description, i believe this illustrates the classical conditioning process known as: spontaneous recovery

Spontaneous recovery refers to the recovery that only happened because of a delayed response after the first conditioning.
When Mariah first 'believe' that her fear of water is gone, it's only happen because there is no actual threat that she face during the swimming lesson, because it's guarded and safe.