I don't think she knew Dawn would use it as a roadmap, but I don't think she thought it would just psychologically satisfy Dawn into giving up the quest, either. I think it intrigued her. I think she knew she should accept Tara's reasoning as morally/ethically sound, but a good Willowy bit of Willow thought it was hogwash, so she was rash, and popped the book out for the kid, not to educate her into giving it up, so much as to educate her, and let the chips fall where they may.
I don't see the intrigue in this instance or letting the chips fall. She'd know that Dawn was incapable of doing this kind of spell properly. It's noted specifically in the script she's attempting solace. Again, I'll say she's being criminally negligent with a minor with dangerous magics, but she's still a minor herself.
I don't think Willow credited Dawn with being determined enough, or resourceful enough to follow the trail.
That's true. Also, she was ignorant that a trail could start with that back (her exchange with Tara shows that she didn't know that book as well as Tara did, or the implications of it being gone).
Most likely, Willow hadn't studied these resurrection issues very deeply then (or later), and she wasn't too concerned. But given she later resurrected Buffy, I really have a hard time believing she was only trying to give Dawn the kind of closure that comes when you decide to give up on something.
I don't think she was attempting to give closure. She instinctively offerred the thing where she had found solace - she always dealt with her own pain by going to magic first.
Willow's brain didn't think that that far through, either. And this is (to me) her interesting flaw. She's a bright, deep thinking woman, but she spends a lot of time in denial and ignorance, because she doesn't want to learn things that she doesn't want to know.
Again, she's very young, which we forget. Even bright 19 y.o.'s are inexperienced and short on judgement (excepting the ones who post here, of course). Plus, she was already way out of her depth without any real guide.
C'mon, Giles spent all of S4 on his ass watching soaps with Spike. He could've spent that time working with Willow. It's a significant failure on his part, and I think he knows it by the time he comes back in "Grave." Not his fault, mind you. Not at all - Willow's responsible for her actions and choices. But he knows he could've done much more. I think he didn't because he didn't want to deal with what was - in essence - a replay of his biggest lapse. His dabbling in dark magic in his youth.