How hard is it for a deaf kid raised with the ASL(sign language) to learn BSL if she's moving to England?

It correlates with how difficult it would be for a kid raised speaking English to a kid who needs to learn to speak in French. If the child had a good handle on the grammar and syntax of spoken English they would have an easier time. ASL was created by a person of French origin and is based on French grammar structure. BSL is based on English. Another difference is one is primarily a one handed alphabet (ASL) and the other two handed (BSL). There are also plentiful language differences in spoken American and British English that must be taken into account. When I made the move I was surprised by how different the two forms of English really are.