I read the cards in the first place to help and heal. I hope you do, too.
As such, I think it's your responsibility to let the seeker know what is happening. After all, that's why she came to you. But you must do it as gently and lovingly as possible. (This is where some training in counseling would help, because that is really what we are doing here.)
Remember to point out that the cards don't say what is going to happen. They say what is likely to happen if nothing changes. It's like standing at the crest of a hill, and looking down a road. If someone is coming up that road, they can't see over the hill. You might call to them, and tell them a car is coming. But if they turn when they hear you say that, or if the car turns into a side street before they get there, they won't ever see it. That doesn't mean it wasn't there. But things change!
I have never seen the cards predict physical death. (They don't seem to care.) Remember that the Death card means sudden change.
I suggest that you talk to the seeker before the reading, and make sure he really wants to know, and that he understands this isn't a game. (If they want to play around, try doing something else.)
Try never to frighten the people who are coming to you. That doesn't help people to change very often. Usually it simply makes them stop listening to you. If they become frightened because of how much you know, or how accurate the reading is, downplay it. I usually make a joke, because it's hard to laugh and be frightened all at once. You will have your own style, but be gentle and calm. Try never to lay out the cards, gasp, and say, "Oh no!"
I usually see if I can get the seeker herself to tell me what is wrong. If you hint, and if you have established that you expect her to work with you before you start, she usually will. People normally know exactly what dark clouds are looming ahead; they just hope they'll go away on their own. And I've found it's lots less frightening for the seeker to tell than to be told.
Be sensitive to the mood and body language of the seeker. Don't push; you don't want to create either resistance or blame here.
I recommend that you not be critical or judgmental, either. This also creates resistance, and doesn't help anyone. Sure, we are each responsible for ourselves; but we also all make mistakes. I assume that you don't want to be slapped around for yours. Assume the same about the seeker.
I also recommend that you don't tell anyone what to do. If you do, there is a tendency for them to do the exact opposite if they don't "believe in this," or follow blindly and blame you if anything goes wrong. Neither action helps anyone. Make suggestions, give them food for thought, but don't dictate even if they ask you to. They have to make their own decisions.
Remember that everyone already knows the best path for themselves, at some level. Even if they seem to be bent on doing something foolish, that may be something they need to live through.
Give the seeker room to find that inner wisdom, and emotional support to take the needed steps, and trust her to find her own way on the path that you have illuminated for her!