I don't know enough about
Sarah to be sure. It's said to mean 'princess' or 'lady', which are hardly the same thing.
Augusta, as the female form of
Augustus, is more of a religious title, something like 'distinguished person', with its origin in the verb augere = to increase (in virtue). So, if
Sarah is secular and
Augusta is, let's say, religious (
Roman religion wasn't much like what we understand by religion today), then putting the two names together would be a bit ambitious but you wouldn't be repeating yourself.