I don't know "Beautiful Girlhood" but from the Amazon reviews, I'd say the two books are quite different.
Before You Meet Prince Charming is half allegory (like a fairy tale) and half discussion/conversation starters. It is very charming and DD looked forward to the next installment each time we read it.
I appreciated that it didn't have the flaws I've found in EVERY OTHER book I've ever read on the subject of courtship/dating/choosing a spouse. Every other book I've ever read had one of two flaws 1) the others were too graphic for young girls - this one is entirely wholesome if the reader is innocent 2)the others considered young men to be naturally immoral and young women to be naturally moral while dating ("watch out for those bad boys! they only want one thing! and YOU are sweet and virtuous and only want love! Don't trust them!" sort of tone) only to say that those same "bad boys" should become head of the family after marriage. Like they somehow magically changed on the wedding day, despite being slime while dating
This book was a delightful read - and focused on the importance of Godliness & character in the young man - and the importance of young women building their own relationship with God before marriage - or even if single for life.
I thought it was a book in its own category - well worth a look. And DD really loved it : )
ETA - I just found Beautiful Girlhood online, and read a couple of excerpts. the two books are VERY different from each other. Tho they're both on the topic of Christian virtue for young women, that seems to be where the similarity stops.