My question is:
1. Is there any way to sponsor my daughter to Canada? If my application gets refused, is there any chance to win an appeal?
You signed the document stating you understood that by not getting her medicals done, you would never be able to sponsor her. These cases do not win. Even on appeal they are virtually always denied.
H & C grounds; getting her in this way is possible, but not likely. If her mom had died and there were no other relatives to take care of her, maybe.
2. What is the reason behind this policy? What difference does it make for my daughter to take the medical exam then vs. now?
Potential immigrants don't have family members examined at the time of application because they think these other family members will hurt their chances of being accepted, for whatever reason. So immigrants get in who otherwise would have been refused. CIC wants to prevent that, so has this draconian policy.
The best way to get her in would be to have her come on a student visa or as a FSW. You can provide the education she would need to get the points necessary for immigrating on her own.