Medical bag restrictions?

My daughter is a type 1 diabetic and will be leaving for a 5 month study abroad experience in Spain this week. She will have a carry on rollerboard suitcase full of medical supplies. I know she’s allowed a medical bag in addition to her normal carryon allowances (one item stowed in the overhead and another, personal item, under her seat). Are there restrictions on the size of the medical bag, aside from regular restrictions of carry on items?

For reference, she’s also planning on bringing a 35l backpack and her school backpack as her other carryon items. She is flying Delta Main from MSP, connecting in AMS with her final destination of Barcelona.

If you have similar experience, are there steps she should go through throughout the checkin and boarding process to make this as seamless as possible?