You need to work out if she's snacking after school because she's hungry, because she's bored or out of habit.
Mine are always starving after school and 6/6.30 would be too late for them to eat. Batch cooking or cooking the night before is how I get round it. The kids eat at 5 eating the meal I make the night before. While they are eating I chat to them while I'm cooking the next nights dinner. DH and I eat together later when he gets home from work. A couple of nights a week they'll have a pudding (not always a sugar laden one) while we're eating so that we can eat together for a bit.
If she's bored then she needs more structure in that hour rather than just being left to her own devices.
In my house my kids were getting an unhealthy attitude to snacks because I had an unhealthy attitude to snacks/food. I didn't binge eat 4 packets of crisps around them, but they were in the house and they knew. They're not daft when they notice there's 3/4 packets of crisps less in the cupboard or several choc biscuits gone they know I've eaten them.
So we have a snack box each. Every Sunday 7 things go in the box. A selection of crisps, chocolate, seeds, poporn (althogh we put a wee bag of kernels in as popcorn doesn't keep well) - anything that's not in the fruit bowl or chopped veg box in the fridge as they are both help theirselves anytime goes in - something can be taken out of the box anytime they want, but it only gets filled on a Sunday.
They also get to choose (mine for example only has crisps in as thats my binge thing) what goes in and the penalties for taking something from someone else's box are very harsh.
The first week was tough, I won't lie. Three people, including me, ate everything in two days. However now we all have a much better attitude to snacking and food in general and mostly the boxes all have leftovers on a Sunday. Plus the children tend to have something when they are hungry rather than because someone else is having something.