The basal / bolus regime which your daughter is on is designed to best mimic the pancreas. The Lantus is the slow acting insulin normally given once or twice daily which deals with the glucose that is drip fed into the blood by the liver. The novorapid ( bolus insulin/fast acting) is given at meal and snack times to deal with the carbohydrate content of the food. If you can let us know at what time of night the hypos occur and when the last novorapid at tea time is given, it may help us work out which insulin needs adjusting.
It is normally a good idea to give a small slow acting carb snack at bedtime especially if her bg is a little on the low side about 4/5, but ideally the background insulin should keep the blood fairly consistent, If you are needing to give more than about 10/15g of carb at bedtime, then it would suggest that the insulin needs some adjustment. Doing the nighttime test will highlight this.
As far as snacks are concerned, you can give non carb snacks at any time and in moderation these would not require any insulin. Some ideas are cheese, meat, chicken drumsticks, pepperoni, salmon flakes and sugar free jelly. Things like strawberries, rAspberries and cucumber are very low in carb, so again in small amounts may be given to your daughter without affecting her bg although you would need to test for this. Carb snacks can also be given but would require an injection of novo rapid to cover the carb content. Because it is early days, it might be better to stick to carbs at meal times only so you are only giving novorapid at mealtimes, this will probably help you achieve better control as you can better understand the affects of insulin given at breakfast, lunch and tea.
Novorpaid has a peaking time of around 2 / 2.5 hours and for most people has finished working after 3/4 hours. if bloods are falling or rising after 4 hours from the last injection, then it is likely to be the lantus that is wrong. I'm afraid this will all be down to trial and error, lots of blood testing and keeping records to refer back to.
I know that all of this sounds daunting, but by testing regularly and keeping records you should hopefully work out doses. As small children are creatures of habit and like to eat the same foods at the same time of day, you should hopefully see a pattern emerging.