There really are many variables to be considered... The first one that comes to my mind is that the P99 just does not fit her... Don't freak out yet, like I said, there are many possibilities...
After renting and borrowing many firearms, my wife settled on a Sig P228. I never figured her for that one.
The second thing that comes to my well scared and dented head is "hold" and "stance". How is she holding the gun. Many people have a problem with hold and stance. I'd like to have a dollar for the number of people I've seen that hold the pistol completely wrong, like the weak hand thumb over the top of the other one... Also make sure the pistol is deep into the web of her hand... Many people try to hold the pistol way too low on the grip...
Also check stance. If you've ever noticed, most people tend to lean backwards when shooting.
You would be amazed at how proper stance can effect recoil... Lean in to the gun, spread your feet about shoulder width, with a somewhat sideways stance, weak foot forward, and let the recoil go through your arms (with strong arm elbow slightly bent), through your torso, and into the ground through your back foot. Might even bend the forward knee just a little... (I know, a picture would speak a lot more clearly, sorry about that!) It's better to exaggerate the stance at first to prove to yourself it works, then you can refine it and smooth it out to where it flat looks and feels great!...
Ok, I'm brain dead now... It's a lot easier to show than to type!