If you haven't done so, I would dissolve the extract in 100% DMSO, and then dilute with water (9 parts water to make a final concentration of 10%). You may still have precipitate depending on the compounds in the extract.
It depends on the type of assay you are trying to perform and the amount of extract you're trying to dissolve. I agree with dissolving it in 100% DMSO then dilute. You can also try shaking, sonication or gently warming the solution.