It's bloody scary although I'm sure they would have kept her in if they had any concerns. Keep an eye on her breathing if you're worried though (over 40/minute is too fast).
You can always take her back if you have any concerns - the A&E paed told me they'd rather parents of small babies err on the side of caution
And welcome, agnes :) I'm an entirely dedicated listener but I've become much more enthusiastic about listening daily (rather than the omnibus) since this thread. It sucks you in!