Stomach bugs are a nightmare in children with diabetes, and since my son was 4 at diagnosis I've sadly had lots of experience at managing them (including 3 bouts when he was on mixes!). The after effects can continue for about 3 weeks after the illness, as the gut is still healing and digestion is slower - leading to lots of hypos.
Frequent testing of her BGs and ketones is a good idea. If she has no appetite, try things like sugary jelly, sugary ice lollies, etc. with small doses of insulin, to keep hydrated and keep clear of ketones. If she is eating, bolus insulin after eating (and at reduced amounts), and if she is on a pump, consider giving meal boluses as a square wave over 30 mins to 1 hour.
Hope she feels better soon 🙂