She probably just has a little bug and will be right as rain in no time, give the doctors a call, you should get an appt today and hopefully that will put your mind at ease.
is baby drinking anything? eating at all? how wet are nappies?
the answer to these will often dictate how quickly you need to seek advice.
hope GP can offer some advice, there are a lot of bugs about
Hoping your baby is now well and back to herself again :)
For the sake of future reference though...babies dehydrate fast and I would not leave it longer than 48 hours regardless of whether it is a bug that will clear up. As always mums know their babies best so don't hesitate if you are worried.
If babies are not interested in drinking or will not drink try using a plastic baby medicine syringe (most chemists will give you one for free) placed inside and to the back of the mouth to gently drizzle the water down their throat. Dont worry about them choking as they will swallow out of instinct.