I phoned the OOH vet at nearly midnight in a fit of PFBness. Vet seems to think to just keep an eye on her at the moment.
She is often sick because she's such a scavenger. We've recently got really dilligent about shutting her out of any room where she could get food and the easter eggs are up on the wardrobe.
But DH and I went out for a meal tonight leaving her with DD2 who said she started being sick about 20 mins after we had gone. She left it on the floor for us to clean up 
(typical teenager!) but that was actually quite useful as I could see what had been thrown up.
It was masses of brown liquid, not much else. I wondered about chocolate poisoning but cannot find any chocolate she could have eaten. DD swears she was just in the room with her.
Dog was very restless and drinking lots but seems to have settled a bit more now. However, she keeps sighing and looking at me as though it is my fault and I have inflicted it on her!
She's my baby and I hate seeing her ill. I like it better when I know what crap she's stolen and therefore why she is sick. I suspect I will be awake watching her for a lot of tonight. 
No real point to this thread, just worried for her and needing to share.