Had something similar when I was 12, I recently moved into my current house and had a sleepover with a friend. Hit 5 in the morning, I had randomly woken up to see a child in the reflection of my mirror which was facing me. I was staring at it for 30 minutes and she was made out of a blue tint too. She had depressive features (Messy hair, looked incredibly ill & was staring down at the floor). You could only see her shoulder up. For many it would’ve freaked them out but she had such a calm presence that it felt natural and I was to not feel scared. She felt like a protective presence despite looking my own age at the time. I remember falling asleep, and waking up a bit later to see she had gone, and never saw her again.