Bottom line: no, we cannot create anything we desire!
On a simple, rational, logical level, anyone can see that's a ridiculous notion. In theory, maybe, but not in practice, and certainly not in practice at the level of development at which most of us are.
However, the main reason we cannot create anything we desire is for the simple reason that as souls incarnating on Earth we choose a path of development, a life purpose. If what we want as human personalities is dramatically different from our already-chosen life course, we will simply not be able to create it no matter how hard we try.
Second reason we can't create anything we desire is because--I think in good manifestation books this is covered--we have beliefs and feelings countering that which we want to create, so they would have to be cleared first before we can create what we want.
Back to Grabhorn's book. Honestly I've never seen more hubris. Her views are stated as fact. Sure we all know something--at this stage of our development--but none of us here on Earth can know the ultimate Truth. Even in our spirit state, how much we know will depend on our development. Therefore truth always changes depending on where we are in our evolution.
So, she states as fact--and this is italicized--how our feelings will always produce reality no exception. False!
There are exceptions, and very important ones. The main exception being that, once again, before incarnation when we choose our learning here on Earth, there are certain territories that will be exempt from the influence of our thoughts and feelings. For example our physical body will not be effected, or certain accidents will not befall us, etc. Why? Because our learning is elsewhere.
That's as far as I got in that book, just briefly leafing through it. It was upsetting to see how many people it might have mislead, not just with this one simple example, but who knows how many others throughout the book.
Bottom line, in my experience, there are things that we know here as humans, and a heck of a lot more that we do not know, way more.
A good way to approach the entire manifestation process is to leave the bigger part of that to our divine self who knows more than our human personality.
If we want to make effort in that direction, clearing ourselves of the lower vibrations such as hate, resentment, jealously, greed, fear . . . and bringing joy, love, peace, beauty, etc., into our lives, is a way to create optimum conditions for our optimum well being and happiness.
And another suggestions: no matter what or who is the authority, always retain the right to be the authority of your own life. If it does not sound right, let it go. If it does not feel right, let it go. Do not make yourself believe things or do things that strongly go against what, in the deepest part of your being, do not sound true or feel right.