Now you’ve put them together then they need to stay together permanently.
Piggies should not be separated at all after they’ve been put together as this stops the whole bonding process, means they haven’t got through the stages, and they’d have to start all over again from the beginning every single time. This is very stressful for them. It takes around two weeks for them to fully bond.
You certainly don’t need to separate them to feed - they will share and the baby needs to learn from the older one.
If things have gone well and they’ve been together in the bonding pen for several hours then you can move them to their cage together. They must not have separate cages at all now
Make sure there is plenty of hay available in multiple places around the cage. She will get plenty of food so don’t worry about that! Ensure you carry out the weekly weight checks throughout their lives as that is the only way to know they are eating well