As English is both a language and nationality, 'an English accent' can be ambiguous - one of the many accents of the language or the accent of that country. So she was probably clarifying that your particular English accent sounds like it is from England rather than, say, from Australia. There is no way in which she is mocking you unless there is more to the context that we don't know.

I'm American, but if we refer to something as 'English English' we mean British/UK/England accented English.

she meant it wasn't Scottish or Welsh