I'm with those who say take advantage of the offer. You know how much you can store, and any surplus can be donated/gifted appropriately. You'll need to consider where you have to sort through things tho - could you go with your friend to the house and sort it there? Might help her be a bit less overwhelmed if she has help, tho of course need sensitivity to the fact that you would be in her mother's house so she may not be keen on this idea. Depends on the people and relationship involved I guess.
But I would say that you are doing the right thing, yes.