The next time she gives you something say Oh .. I don't think I can make use of this but I know someone who can , and give her a name of an organization or person who could use it.
To continue to take it is not a good solution since she will continue the good deed thinking she is actaully giving you something you want and will make use of.
I share some of my supplies with others but I would be dissappointed if they never really had a use and just kept accepting. I could have directed my donations to someone who truley would want and make use of them.
She may be offering these as a form of gratitude for your friendship. I think this has become an obsticle for you , in that you think the motive for the giving has not revealed itself , so redirect this giving .