People do seem unable to separate Andraste the person from Andraste the icon of the Chantry. Andraste certainly existed as historical fact. Her Exalted March with Maferath was historical fact. Her death on a pyre in Tevinter was historical fact. Beyond that much else is conjecture.
Her sayings were largely written down after her death by her disciples and this is what became the Chant of Light. Since these vary in style and content, they may not actually reflect her sayings but how her disciples interpreted them. There are also versus that seem more a recording of events associated with her or her followers, like the Canticle of Shartan, which the Chantry later ruled as heretical. The core of the Chant of Light seems to be moral guidelines for a just society which I don't have a problem with. I just object to the way the Chantry has twisted certain aspects and interpreted it to suit their own purpose, in particular the lines concerning mages. There is nothing in the Chant of Light that I have read that says Andraste condemned mages. What she condemned was the abuse of magical power, such as that of the Tevinter Magisters she was opposing.
I have noticed people stating that if they were playing elves or dwarves they destroyed the ashes in Origins because they opposed her religion. This strikes me as somewhat odd since you don't have to believe in the Maker for the ashes to work and whilst a dwarf might have no reason to revere Andraste, an elf, even a Dalish elf, should respect her remains because if it had not been for her (and Shartan) there would have been no Dales. If you oppose her religion, why help a mutated cult of that religion? Still that is simply my take on it.
If the shade of Andraste really did appear to you that would seem to confirm her statements about the Maker rather than the opposite, unless of course the shade actually told you that everything the Chantry claimed she spoke was in fact hogwash. If it really was Andraste I think it would be rather unwise trying to kill her because a) you wouldn't be able to and
it might really annoy her.
Still everyone seems to be assuming that the glowing figure we see in the trailer is meant to be Andraste. I think it is more likely that certain members of the Inquisition interpret what you have seen according to their beliefs. If the spirit really had announced itself as Andraste I think the Inquisitor would be rather less vague about how they survived the big bang at the beginning. So it's more a case of "I saw this shining white being which touched me" and Cassandra/Cullen/Leliana saying "Oh you've been touched by the shade of Andraste".