let her rip

let (something) rip

1. To let something go; to start something up. Often used as an imperative. OK, the rocket is ready to launch. Let that thing rip! I replaced the spark plug, so go ahead and let it rip so we can see if there's any difference. We've spent so long working on this ad campaign that I'm excited to finally let it rip.
2. To do something without inhibition or restraint, typically with great enthusiasm or force. Wow, did you see that kick? He really let it rip. When I'm writing a first draft, I like to just let it rip and not worry about typos or grammar.
See also: let, rip

let her rip

1. To let it go; to start it up. Often used as an imperative. "Her" is used in the same way that some ships and machines are referred to as female. OK, the rocket is ready to launch. Let her rip! I replaced the spark plug, so go ahead and let her rip so we can see if there's any difference. We've spent so long working on this ad campaign that I'm excited to finally let her rip.
2. To do something without inhibition or restraint, typically with great enthusiasm or force. Wow, did you see that kick? He really let her rip. When I'm writing a first draft, I like to just let her rip and not worry about typos or grammar.
See also: let, rip
Farlex Dictionary of Idioms.

Let her rip!

 and Let it roll!
Inf. Let it go!; Let it start! Time to start. Let her rip! There's the signal! Let it roll!
See also: let
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.

Let her rip!

and Let it roll!
exclam. Let it go!; Let it start! Time to start. Let her rip! Let’s go. Let it roll!
See also: let
McGraw-Hill's Dictionary of American Slang and Colloquial Expressions

let her rip

Allow an engine to go as fast as possible. An American colloquialism dating from the first half of the nineteenth century, this term presumably was first applied to locomotive or steamship engines. The American journalist Park Benjamin recorded it about 1840: “Another phrase, which often glides in music from the lip, is one of fine significance and beauty, ‘Let her rip!’”
See also: let, rip
The Dictionary of Clichés by Christine Ammer
See also:
  • let (something) rip
  • let it rip
  • let rip
  • let something rip
  • let it roll
  • Let it roll!
  • let in
  • let us (do something)
  • Let us do
  • let the grass grow under (one's) feet
References in classic literature
Wait is what I say; but when the time comes, why, let her rip!"
Treasure Island
'darn please,' and 'cut your cable' is decidedly preferable to 'let her rip.' I once made a rule that I would have no slang in the house.
Eight Cousins
As for this thing, why, it has no nerves, no delicate joints nor tendons; it's a case of let her rip."
The Valley of the Moon
He should be beaten with a bat or put in a room with a vicious dog (maybe the puppy's mother) and let her rip him to shreds!
Mama knows best
a I just let her rip and praise the Lord, it went far."
Hill climbs to top after `clumsy' year
I know Paul O'Grady's put her to rest - apparently she's in a nunnery somewhere - but I'd let her rip me apart.
showbiz: A WEEK IN QUOTES
Turn off the hi-fi, open the windows and let her rip!
VW Golf R32 V6 4MOTION; TESTED
"Let her rip!" The local sheriff botched the job, however, and he was actually beheaded on the gibbet.
Racing: WHAT'S IN A NAME? Black Jack Ketchum (SunAlliance Hurdle, Britannia Insurance Hurdle)
As he quartered away, I drew back my bow, settled my pin into the front shoulder and let her rip. My arrow found its mark to the buck's chest.
Polished mulie
Had nobody the imagination to put Linehan in his alter-ego Mae McFettridge gear and let HER rip at the festival?
SHANE ON THE SCREEN: Dumb show