they are essentially the same medication - just in different release mechanisms - so should be no problem as far as taking them at the same time.
and it is not uncommon to add Adderall in the late afternoon to extend the helpful benefits.
However, this (without having more info) does sound like she could be getting an overdose. Vyvanse should last close to 10+ hours. If it does not, its an underdose. Adderall IR lasts 4 to 6 hours and XR 8 to 10 hours.
The big question is when is the misbehaving happening? This would give you an idea of (if it is an overdose) when to adjust the medication.
Also keep in mind that lack of sleep can really effect a child. Also, just school pressure can do the same. And, if the misbehaving is happening right after school - it is not unusual for a child to have to blow off steam after holding it together all day long. thats why it is important to come home and have some free time and physical activity.
Any way, it is very important for your friend to talk to her doctor and get their input.
Hope this helps. If you need any more information - please post. Best wishes.