Dear Patio Lover,
That sounds wonderful! But yes, I can see that a daily soaking is not good for your deck and equally bad for your moral. It's possible this neighbor doesn't even realize that her hose addiction is causing you inconvenience. It sounds like you already have a good relationship with her so maybe you should try something a little sneaky: Invite her over for a glass of wine one evening on your deck. She'll quickly notice the problem and you may not need to bring it up at all. If she says anything about the water pooling on her chair though, feel free to casually say, "yes, I'm a little concerned about the water damaging the deck!" She could easily switch from spraying down everything in hose range to a more precise watering can.
I doubt you'll need to proceed further but as a last resort, I'm sure your landlord wouldn't be thrilled to learn that his property is being damaged and would probably put a stop to it immediately.
Enjoy your new deck this summer!