Caught My Teen's Secret Note

So I was going through my daughter's room yesterday, and found a note tucked away in her pillowcase. It turns out she wrote this sweet little love letter to her best friend from school, talking about how much she cares for them and wants to give them flowers. I didn't read the whole thing because I felt bad, but part of me just had to know what it was about. Now I'm wondering if it's okay that I peeked, or should I talk to her about my nosiness? Have any parents out there dealt with something like this? Is it normal for a parent to feel so curious and unsure?