H.K.
Hi J.!
I worked with 2 year olds for a long time. Biting is a phase that some of them go through. However, excessive biting can become a bit of a problem. It sounds like you are doing everything right with the extra special attention and all. I would take it a step further and have her do the first aid for her brother (wash, and apply ice).
One thing that I found helpful is to write down when she is biting. Is it before nap? snack time? some children bite during transition periods between activities so knowing what triggers her biting can be really helpful.
Something that helped some of the other biters was re-introducing a pacifier or bottle (i know it sucks but biting is dangerous especially if they are breaking the skin)
Also I had one incident where a child was biting ALL the time. turns out that he had a sensory deprivation issue and when someone was in his personal space he bit.
Just keep re-inforcing the nice touches and use of words and it will all work out.
Don't forget to let us know what happened!
H.