Keep it simple. Have you done a mandatory reconsideration? If not you have one month from the date of the PIP decision. You can do it in writing or over the phone and you do not need new or new medical evidence to do it. The chances of success remain limited so you will most likely have to then appeal to an independent tribunal.
Have you self-assessed i.e. sat down and figured out what points she ought to score and why? If you haven't then do so so that you know what your case is. Then be brutally honest and play devils advocate whilst looking at what evidence you have to support the case for the points you think ought to be scored. After that it's a case of looking how to fill the evidential gaps you identify (and most likely there are usually lots when you look at it this way). Mostly it will be a very detailed version of what you just put in your first post.
I'd look at daily living 3, 4, 5 and 6 and I'd concentrate on whether she can do those things safely, reliably or in a reasonable time.