Karen,
I had an unusual side effect similar to your sister's. I had terrible, terrible, PAINFUL itching. The nurse told me to use over the counter anti-itch creams. I also was prescribed some sort of anti-histamine. None of these things worked at all. The nurse told me there was nothing they could do and that they would not lower my chemo dose.
I got to the point that I couldn't take it anymore. My feet were on fire and the itch was all through my body, including buttocks and vagina. It wasn't like a mosquito bite itch. It was a painful sort of itch. I felt I needed to stop chemo due to this.
It wasn't until I changed oncologists that I got some relief. He prescribed me Lyrica. It did not take the problem away 100% but it brought it under control and made it more bearable for me to finish out my chemo treatments.
The only thing that took it away completely was being off of chemo for about 6 weeks. Thankfully, all of this burning went away by that time.
I hope this helps.
MaryAnn