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Thanks all for your help. The problem is not related to her stomach being empty. She is fine overnight, but generally throws up at 4pm, after being fed at noon. I'm not keen on having any further investigation done, if this is how she is so be it.
Kita, I note you had this problem for quite a long time, maybe I will be the same. The old biddy is fast asleep on her duvet now, not a care in the world. If she's happy, i'm happy.
Thanks, Wendy and Megxx