Hi Tanya,
Sounds like you are doing a great job, and what is happening is normal.
IMO memorization is good mental muscle work. Definately memorize scripture, especially the verses/passages that are personal or meaningful. They are the ones that will be remembered long term, even if not word for word the meaning will be remembered. It is probably best to use the Bible translation most appealing to your daughter.
Singing helps with memory work – we all forget most of what we learned in highschool, but can sing those songs we heard every day on the radio! Are you using hymn studies, or any other vocal music?
Poetry is great for memorization. Also famous speeches. I don’t think it is expected that they be recalled long term, although it is amazing what the mind chooses to recall or forget.
In the long run, most information like dates may be remembered while they are the topic of study, but after that what is important is the ability to research, to locate the information. With great living books to glean information, it should be easier and more enjoyable to find these new, or forgotten facts.
Hope I am reassuring you and your daughter that memorization is valuable, yet it’s okay for the mind to let something go.
HTH, Vanessa