Told and have told

Hi there.

I wrote a children´s book (8 years and older) in German and want to publish it in English as well.

It is about adoption. The little girl has been dreaming about her birth mom and when her adoptive mother asks her: "How long have you been dreaming about that?", she answers: "I am not sure. I think since you told me about her."
Is that correct?
At first, I wanted to write "I think since you have told me that she had brought me into this world." But then I thougt that the sentence was too confusing and too long. Moreover, the moment of the telling was already over and "since" usually refers to a specific point in time in the past. Therefore, I used "since you told me" and replaced "that she had brought me into this world" with a simple "about her". But it still doesn´t feel completely right, because the telling still has an impact on the little girl (the dreaming). As you can see, I am pretty confused and still not sure whether "since you told me" or "since you have told me" is correct in that sentence.

Thank you for your help!

And another question: The litte girl meets someone who explains adoption and the whole sitiuation to her, thereby telling her something that she absolutely cannot believe. She is very surprised and almost bewildered.

In German, I use an expression, describing her eyes becoming very huge. But, in English I can´t really find the right words. Does it make sense to say: "Her eyes became huge"? It somehow does not sound right in English. What could I say instead? Maybe something like "She couldn´t believe her ears" or "She was in complete amazement"? I also don´t want it to sound too grown up for a children´s book.

I hope that makes sense. Thank you so much!!

All the best,
Katharina