I would respond with "oops, looks like your email got hacked!" even if you don't think it was really spam. It conveys that you don't think it's something she would ever legitimately send. Her response to you, I think, will inform your next reply. If she takes the out, then I'd move on with no hard feelings. If she insists "No, I meant it for you, I thought it would be helpful!", then I would say outright, "That's very hurtful. I'm very upset you would send something like that to me."