I know you are concerned about your grandaughter's safety and wellbeing, but this doctor/surgeon does this for a living and I'm sure he prescribes this for all of his patients. I can tell you that I had to watch my son endure the pain after his tonsilectomy and the syrup with codiene they gave him didn't touch the pain he had. I felt helpless.
I do understand your concern however, but loracet is basically vicodin, and should be safe for your grandaughter. It will be so much easier on her if she can be kept as comfortable as possible, because crying from the pain can cause so much more pain and possible complications from all that straining from crying.
If you are truly concerned, you can call the pharmacy and ask to speak with a pharmacist and he/she can tell you the safe/common dosing for children weighing 25 lbs.
I do hope your grandaughter will have a speedy recovery. I feel for any child having to deal with that pain, and also feel for any parent who has to feel so helpless while trying to help their child through the painful recovery. Take care.