Both Anne of Brittany and Mary Queen of Scots were young female rulers who happened to be married to a Valois King of France following an external war. However, Anne de Beaujeu and Charles VIII required Anne of Brittany to marry Charles VIII's successor, while Charles de Guise and Henri II explicitly allowed Mary Queen of Scots to return to Scotland to remarry in the public treaty(the Crown matrimonial to Francois II, which was in the secret treaty, wasn't actually ratified by Scottish Parliament, thus died with Francois II himself).

The scenarios were very similar in some ways: Charles de Guise feared the ascendancy of Prince Conde and Earl of Arran, while Anne de Beaujeu feared the emergence of another Habsburg branch in Brittany or the Duke of Orleans as a significant power; Charles VIII wanted to consolidate France, Henri II and Charles de Guise wanted to create a trans-Channel Empire from the Orkney Isle to the Pyrenees. Why didn't Charles de Guise seek to bind Mary Queen of Scots in France through the public treaty, as the example of Anne of Brittany was already on his hands, and why didn't Charles VIII allow Anne to return to Brittany to rule as a sovereign duchess(as Brittany de facto was prior to 1491) after he died?