The Universe Against Her was first published in 1964. It consists of two episodes which can be regarded as the first two Telsey Amberdon adventures. Despite the juvenile title (and equally silly pictures on the front of the book), I found this to be a great read. If you're new to Schmitz, this book would be a very good place to start.
The first of the two episodes describes how a very young Telsey first learns about her psionic ability, which then allows her to overcome several obstacles and avert an impending disaster. The second episode involves Telsey working to gain greater control over her new-found talent and struggling to avoid being a tool of the powerful Psychology Service.
The cover shown is from the ACE fourth printing in 1984, cover art by Steve Durke.