After you talk to her, head up the tower. If you haven't learned to stealth well up until this point your reckoning is at hand.
First goal is the spiky haired undead who patrols from the right of the tower to the entrance. After you get the key from him, stealth and start your way up the tower. The mobs in here aren't THAT bad, but mid-way up the tower they start appearing in groups (of two I believe).
Once you're at the top you'll see Klaven. Don't attack him or let him see you. I have no idea what lvl scale he's working from, but even though it says he's a lvl 22 (i think) elite he hits MUCH harder. Do not try to trifle with him. Just wait for him to go to the other side of the top, run your stealthed self toward the chest, pick it, steal the book.
Alternately (and i would suggest this)- stay stealthed next to the chest and pick it for as long as it takes to max out your skill for your level. You'll get diseased by picking the chest, but don't get cured of it. Head back to SW because it starts a pretty funny quest to get cured.
/tutorial off