I dont think this argument makes much sense to me. Her grandmother was there for her and she loved her. That alone is reason enough to keep a memento of her. You dont need to dramatically throw away something that reminds you about a dead family member just because your opinions come to differ over time. Even if she ended up being disillusioned with the idea of finding true love, her grandmother's words were made with good intentions and were filled with love and she was a family member Alex cherished. So I see no reason for her to have that flashback rebelling against her grandma being all dramatic if she naturally came to disagree with an opinion her grandmother had over time as Alex grew older.Again, if she did that then that should've been shown in a flashback where, say, she threw off her cross at some point (which would be a strong indicator of her rebelling against her grandma or her "growing up" from her Nana's teachings/memories, the Prince Charming tale included). But at no point did that ever show up, even during an opportune moment (the Ulysses party heart-to-heart).
As a real life example, my opinions on certain political topics differ from that of my parents. But I still love them - its not an act of rebellion just because our perspectives are slightly different.