I'm guessing that they could have found an older woman with some sense and experience, even if she didn't have perfect English.
It is very important to some parents that the person they hire speaks English fluently. If parents are going to be working long hours, and they want their children to acquire English as a first language in an optimal environment, then hiring someone who speaks Polish or Spanish or non-standard English as their first language isn't going to work.
99% of the people who apply for nanny jobs are going to work out fine. The majority will have multiple references and solid experience. This is because huge number of American teenagers babysit during their teen years and have a lot of experience taking care of babies and children both doing evening babysitting and during the long summer holidays, even when under 16, which is when American teens can be hired by local businesses in many states. Teens who keep up their babysitting clients after that are usually pretty dedicated to the job and enjoy it.
My own DCs did mothers' helping from about age 12-13, progressing to babysitting on their own in the early teen years. They all spent summers taking care of children, bringing them to the pool and home, to the playgrounds, making lunch, bringing them to scheduled activities, and more. Some of the families they babysat for were as big as our own. Sometimes an older sister passed a family down to a younger sister. They all babysat in the evenings throughout the school year, making enough to afford a lot of their clothes, and even laptops, etc.