but what's more important: why does the registry exist at all? Because it's something the person really wants? Because it helps guests buy something without having to think about it? I'd say usualy the latter. In that case: by all means buy something you know she'll like. A personal gift is always better, especially if you're close.
(And besides: if you're close: how wrong can you really go - it's not like a bad gift will ruining a good relationship.)