It's an odd expression; it seems to be based on the belief that a basket of fruit is an appropriate gesture of gratitude - which I guess it may be in that world. If it is a recognized/conventional expression of gratitude, then a bigger one would express greater gratitude. In that case, she's saying 'I want to buy you a huge basket of fruit, as I'm so grateful. But I’m not sure there’s a fruit basket big enough to do that.. Perhaps she trails off before reaching the end of the sentence because she realizes how embarrassingly lame it sounds!
Student or Learner