She's been more than a bit inconsiderate.
I would have been so upset and furious.
She might not have wanted to upset you by asking about the scan picture, but why on earth would she not just leave it where it was until you made up your own mind what to do with it?
What harm was it doing sitting inside a book, inside a box, waiting for you to feel ready to sort through the things and decide what you wanted to do in your own time?
And how dare she use your book?
When you go through a loss, these kind of things matter, even if it's too painful at first to keep things or look at them. That book was a memento of your first child, it was up to you to decide if you wanted to keep it the way it was on the day you lost your baby, use it for your next child, or throw it away.
It was not up to her to rifle though the belongings you'd asked her to store for you, picking and choosing what she wanted to keep, throw away, or make use of herself.
And then to blame you for being upset like last time as the reason she acted without speaking to you about it.
She's been a bitch. She had no right to use or discard any of those things. If her issue was not wanting to store your things then she could and should have asked your DH to take the box back and put it away somewhere else until you were ready to look through it.
My PIL's asked for pictures of our daughter, who was premature and died just a couple of hours after she was born, and then lost them. They proudly announced months later that they'd found them again in a box of rubbish they were about to take to the tip. I can't tell you how hurt and angry I was at them. We had hardly any pictures of her as the camera wasn't working properly, and they took some of the most precious ones we had and treated them like bits of rubbish.
I don't know what goes through some people's heads, but it's certainly not anything to do with empathy or understanding of someone grieving for a lost child.
I'm so sorry for your loss OP, and for the way this woman has treated you. 