Earlier in the day, Lyra had been transformed into Tina's new 'intimate member'. At first, it was fun, but the novelty quickly faded as she struggled with the helplessness of her new form. By midday, Lyra asked Quyz if she could switch roles with Tina and be the one with arms and legs for the rest of the day.
Unfortunately, fresh transformations can't be modified so easily. The Professor, sympathetic to her plight, did what he could under the circumstances.
Lyra now has full control and physical sensation from Tina's body, but her own body is still just as... sensitive.