Insulin roatation and I port Injection port

First…has any used the I Port Inject Port? Are they worth it?
Second…my daughter was diagnosed 6 months ago and we have had a routine of injecting in the back of left arm, Right arm, right stomach and left stomach. We do on use the same site 2 days in a row. But now the doc say the back of her arms have building up fat. I don’t understand this. Its not like it a lump it more like almost the whole upper back side of her arms. Does this make sense. We have avoided the legs because it cause extreme pain 50% of the time.
We have started doing the butt more but she really does not like it. I thought if you did only on injection in a site a day it would not build up?