Regular Babysitter For Wonderful Foster Son Who Has Some Challenging Behaviors

My sister is an incredible foster mom to a wonderful 5-year-old boy. However, she is a single mom and parenting is exhausting so I would love to gift her a regular (every week or every 2 weeks) babysitter so she can have some recharge time. Her foster son is warm, friendly and chatty, but has some behavioral challenges (yells when excited) and is likely on the autism spectrum. We would prefer someone who has worked with special needs kids before.