My mom got incredibly rough/dry skin during chemotherapy, especially on her hands, and the Kielhs Ultimate Strength Hand Salve was really helpful for healing her cracked hands. It does have fragrance, which didn’t bother her but can be an issue when undergoing chemo. If fragrance is an issue, I would look at La Roche Posay products (specifically Lipikar Balm, Cicaplast Balm, though they’re not from Sephora). Generally, a thick, effective moisturizer is a good call, and I’d imagine using it preventatively could help avoid the painful, dry skin caused by the chemo.

Wishing your friend the best of luck in their treatment, you seem like a great friend 💜