My granddaughter is 8 yrs old and has sucked her thumb forever; for at least the last year, we tried to get her to stop, using a mitten, bandaids, duct tape, rewards etc. her permanent teeth are coming in very large and spacey. what to do?

Use the appliance...: As much as i hate having to use these, i would tend to lean toward an appliance if the habit is continuing through 8 years old. The appliances do affect speech since they get in the way of the tongue, so this might be a good motivation for your granddaughter since she won't want to have to speak with a heavy lisp for 6-10 months at school & have to explain to her classmates why she has this.

Mavala Stop: I have had good luck using mavala stop. It is nasty and seems to work well. It is worth a try before the appliance.

Pernicious thumb: Your granddaughter is literally bending her upper jaw bone. Please see an Orthodontist (she's a year overdue anyway) for physical help. Please see a mental health professional to deal with the reason your granddaughter needs her thumb as a crutch.