Two suggestions:

Could she have thrush? It makes nipples crack and slow to heal?

Can she twist the breast/nipple so when baby attached it misses the crack? I had a bad crack with dd and it wasn't thrush but every feed it would open again. Even expressing with a pump made it open. The only solution was twisting my breast so she missed it. It was better to feed and healed faster then.

Good old sunlight helps, so I imagine uv lamps would?