Well, if it was me, I would inject. Diabetes is hard enough as it is, without a strict regime of food/meals etc. Sometimes it's just not practical to eat 3 meals a day at set times.
I would keep counting the carbs for snacks in the same ratio as you usually use. I would certainly test more to make sure you maintain control in the early days so you know which foods do what/when to your daughter.
Also, I'm not a doc, I'm telling you what I would do. If I were you, I would just inform your health care providers of your plans and to ask their advice too. Good luck and please let us know how she gets on ;-)