My niece is the same age and driving her mum crazy too! She is an only child though with a single mum and she knows exactly what strings to pull!

I would most definately keep pointing out that she is the big sister and how important that is in the family but also, I would be pulling anything she climbs on in her room straight out of there and then explain that she needs to earn them back! Its a hard age! Hormones atart to kick in and they arent sure of who they are anymore!

Good luck!