A Landlord does not by law have to insure a building but most do for the same reason that most people insure anything of value, if they have a mortgage on the property or let through an agent it may be a term that their property is insured, but not the possessions of their tenants whose responsibility it is to insure their own possessions.
I would advise your friend to make a claim on her own insurance, if she has arranged insurance, informing the Insurer of how the damage occurred, the insurer will probably wish to recover any payment they may make from the party who caused the damage. If your friend also has no insurance she will have to try to recover the cost of damaged possessions directly from the party who caused the damage as will the Landlord if he has no insurance and there is damage to the building.