Verb
let her rip (third-person singular simple present lets her rip, present participle letting her rip, simple past and past participle let her rip)
(informal) To set off or allow to begin.
Once we have the tank full we will back away and you can let her rip.
Plots and character don't make life. Life is here and now, anytime you say the word, anytime you let her rip. Henry Miller