Giving a dryad a planted sapling should make it sprout instantly
Also, giving a dryad 1L of spring water should allow it to heal your biggest wound by a large percentage
One-time use per individual dryad that spawns
I'd say that it should also grow crops when its runs over them, but that would just lead to herding them into a box and spamming crops for quality
Also please add a lore event for seeing one on your screen (if there already is one I'm sorry but I just haven't seen it pop up for me)