I agree with the assessment that neither Uriel nor Mab were lying. Mab stated that Harry was free to mold as she pleases, which is not a lie. The implication that she has utter control over him is made, but implying something false is not blocked by her inability to lie. We are molded by our experiences, and she will be significantly involved in Dresden's future experiences. Therefore, she will be able to mold him. Uriel's statement "lies" was probably more focused on the implication that he had lost his free will to her desires.
I have a hard time believing that "the parasite" is lash. We've got two gaint powers in the Dresdenverse keeping him alive: Mab and Demonreach. Are we really to believe that these two extremely powerful beings needed the help of some puny hallucination Dresden dreamed up so that he could imagine he was taking a hot shower instead of an ice cold one? I think the parasite will be on roughly even strength to Mab and Demonreach, otherwise it wouldn't have been worth mentioning. (note: I noticed someone posted something about there being a WoJ on the subject. would they be willing to post it? I haven't been able to find it.)
As for the cheater who wispered to Dresden. (begin crazy and probably wrong theory here) Uriel mentioned it was "A being who could know a mortal's entire life." etc. Lash certainly did know Harry's life well, and Laciel herself has spent a significant amount of time on earth manipulating mortals. Plus, she is known for being the most "rebellious" among the Denarians. Even maybe willing to cheat by wispering a few words into Harry's ear in revenge for mutilating her shadow. In one of the WoJ, he pretty much states that Harry actually changed Lash before she died. Imagine the insult that must have been. An Immortal being, overcome by a mortal. And not only that, but he was able to convert her trusty minon into a being with free will. She'd have been pissed, and willing to bend a few rules for revenge.
And As far as getting into the chuch, isn't she already there? Locked inside her coin? or was she transferred somewhere else?
EDIT: Corrected the name of the Island.