Final answer:
The most likely diagnosis for the described symptoms and regression in abilities in the 2-year-old girl is Rett's Disorder.
Step-by-step explanation:
The most likely diagnosis for the 2-year-old girl who has no functional language, does not respond to prompts from her mother, and engages in hand-wringing behaviors while appearing listless is Rett's Disorder (A). This condition is characterized by a period of normal development followed by a loss of skills, including motor and language abilities, which seem to fit the description provided by the mother who states that her daughter 'used to play and now she can’t even feed herself.'
While the other options such as Autistic Disorder (B), Childhood Disintegrative Disorder (C), and Mixed Receptive-Expressive Language Disorder (D) are also developmental disorders that impact communication and behavior, the specific pattern of regression seen in this case is most indicative of Rett's Disorder.