To be fair to Becky, there has to be thousands of dollars of books in that house.
I counted 120 books in this picture alone. This is probably an underestimate, because the skinnier books blend in with each other. The picture is too blury to do a direct price match, so I just used $18.99 as a quick and dirty average. There is 2,278 dollars worth of books in this room alone. A lot of those books are hardcovers and comics, so the actual price could be even higher. Also, Becky has a taste in overpriced woke books. Even the paperbacks are likely on the pricier side too. This picture was also from four years ago. Who knows how much more they've accumulated since then.
Especially since Daniel was regularly dropping 120 bucks on books.
I think she is most likely fibbing. Becky has never valued a dollar in her life. I could see her abandoning those books in favor of an easier move any day. It gives her an excuse to go shopping after all. But Good on Daniel if he actually grew a pair and fucked her over