IMO, 8.5 hrs is really really pushing it for a shih tzu (or any other small breed dog) to hold it. Their bladders are just small. A house broken dog may be able to do it, but training a puppy probably won't go well.
If you are willing to go the puddle pad route (so she can go in a designated area in the house) then you may be able to work it out better. (I'm not a huge fan of this as a long term solution mainly because my only experience with it used as such led to dogs that pee everywhere in the house (BUT, this could be more of a training issue than an insurmountable flaw in the usage, but I do think it leads to more complicated training than just being able to take them out).
Being alone for long periods is not necessarily insurmountable in my mind, but you do need to select the type of dog and individual personality to suit this situation. I'd also STRONGLY encourage having multiple dogs in this situation as they'll keep each other company and busy.
Your biggest hurdle will be training while being gone for such long periods (and exercise, but that's not such a big deal for a shih tzu). You can't really expect training a puppy to go well under such circumstances. Finding an older dog (that doesn't necessarily mean old, mind you) that already has an understanding of basic potty rules and basic manners might be better for you. Finding a bonded pair (that's typically harder for a rescue to place) may be ideal for all involved.