We are currently using RTR and are enjoying it so much! I'm sure you will too when the time comes for you to use it.
Both my boys think the history reading is easier to comprehend this year in RTR than it was last year in CTC.

I don't know why, but it could be that CTC was the first year for them to read the history on their own, so naturally it took a while to develop the comprehension skills. I also think The Story of the Ancient World can be a little difficult to read/comprehend because of the style of language used, but it is a wonderful resource, especially when combined with the Family Illustrated Bible. The readings really reinforce one another.
I wouldn't stress about it.

You have a lot of time until you begin RTR. Your dd will grow so much skill wise this year that I think you will be pleasantly surprised when you begin RTR how ready she will be.
Hope this helps a little. Sometimes all we need is a little encouragement and a lot of prayer.
Allison