Your sister could advertise on freecycle, some people have wood pellet burners and this would burn well.
It can be mixed into soil in the garden, however it can sometimes draw out nitrogen so its best to add nitrogen to the mix too.
Farmers use it for bedding for ducks/hens etc. Rabbits also need wood chips/shavings for bedding and get great warmth from it. They can also use them for cattle and horses for wood chip pads to help underfoot.