I have front splits fast and core stability and training turnout in addition to the perfect pointe book.
For me, I really need to work through most of this stuff with a teacher to really get the details right, but they were interesting reads nonetheless.
I think front splits fast is the most accessible without a teacher after the perfect pointe book and it also gives you access to lots of videos. But if your flexibility training works for you, you don't really have a need for it.
Core stability also has some videos in its members area but training turnout has none. Both of these I feel are interesting reads but I wasn't able to use much of the content initially - I am now that I've worked on some of this stuff with a teacher.
Tbh, I'm not so much a fan of her books anymore (but still very much of her content in general and her videos in particular) because there's a better one that covers all of these topics really well - for the price of one of the Lisa Howell ones if you go e-book: Dance medicine in practice by Liane Simmel https://www.amazon.com/Dance-Medicine-Practice-Prevention-Training/dp/0415809398
But I guess it also helps that Liane Simmel is my teacher's teacher so anything in that book ties in really well with what I'm learning in class.