This book is both hilarious and terrible: hilarible, shall we say. This is as it should be. It is meant to be a Sweet Valley book, after all, and if you do not think those books are hilarible, you are misremembering or kidding yourself.
It is written in the present tense, except for where it is written in the past and the perfect tense to create whole Russian nesting dolls of ridiculousness, a lot of which I assumed were references to the (many, many) Sweet Valley books I haven't read, but much of which turned out on reading other reviews to be original to this book. The finest piece of intertextuality, for my money, is the extensive revisiting/retconning of Dear Sister from Jessica's perspective, where she is represented to have a discernible thought process instead of just being a mindless shit-stirring hobgoblin. I don't buy it for a second, but it's a valiant effort.
Jess has finally succeeded in stealing the hapless Todd from her sister, which, in turn, is apparently what Liz needed to finally acknowledge that her sister is a raving sociopath. While Liz struggles as a theatre reviewer in New York (which is apparently outside the magical bubble of Sweet Valley where being a Wakefield means that you succeed at everything), Jess mopes about being a terrible person and missing her twin and her sweet, sweet enabling. Stuff happens, and finally Elizabeth has an epiphany: Jessica can keep Todd, because she is going to marry her best friend and silently devoted lover ... Bruce Patman. Yes. This is the best crack pairing of all time