That is just plain stupid. She has proof of her feelings: Her feelings; she may be a hard-core, dyed-in-the-wool solipsist, and she will still have her feelings as something real that she knows exists. A supernatural entity is not her feelings and the analogy is wholly inappropriate—to the point of being ridiculous.
Hence, you believe in Odin, Zeus, and the Invisible Pink Unicorn. They’re all beyond “this physical world” just as much as your “god-force.” Indeed, you’ve completely scrapped god for a “force,” one which one can feel, by your own claim, and therefore must interact with this physical world, in direct contradiction to your claim that it is beyond it.
But let’s consider your claim that this “god-force” is unprovable. That means that it has no physical footprint in this universe. Physicists are on their way to determining the actual shape of the universe. They may be a way off, but they’re actually working on the mathematics and observations necessary to come to a prima facie, if not mathematical, proof of whether the universe is shaped like the surface of a doughnut, a saddle, or a plane, but in who knows how many dimensions. In spite of the fact that we can get to work on something so awe inspiringly subtle, it still remains that your “god-force” cannot be proven. (Apart from being able to feel it, of course. Gosh, it sure would be nice if we could make an experimental test based on that!) So, you’ve abandoned god in favor of a “god-force,” and this “god-force” is wholly separated from the universe—except for how it affects your feelings.
How is it that something that is beyond the physical world and is unprovable, is also so obvious and intrusive that we can feel it? How does it initiate neural-chemical reactions without violating energy conservation? And if you’ve abandoned god for a “force,” whatever that means, why bother believing at all?
To the OP, there is no reason to prove atheism. As an atheist, I am merely saying that I don’t believe in the supernatural, whether one claims it is manifested through Yaweh, the influence of the signs of the zodiac, or a god-force. If you tell me that smoking causes cancer, I don’t believe it until you provide proof. It’s not up to me to provide proof of the contrary until you make a prima facie case for the link between the two.
Similarly, there is no reason for an atheist to have an argument against theism. She may, if the situation calls for it, make an argument against alleged proof of a certain theistic claim. For example, one may claim that one’s religion is real because one feels her relationship with her god. It is reasonable to then point out that the same can be said of adherents of myriad supernatural belief systems, and if her evidence is valid, then so is theirs. (Note that she is using her feelings to prove the supernatural, not to prove her feelings.) If any of these are incompatible, then her proof is shot. It can also be pointed out that she is begging the question: Her feelings, if sincere, don’t prove something. Heck, I’m sure we can find someone who feels that O.J. didn’t do it, or that the moon landing was a hoax, or that Elvis is still alive. How is it that their feelings become evidence in favor of some external fact?
One may also discredit a particular system of belief without putting forth an argument against theology in general. If one claims that her god is love, is infinitely merciful, and sends sinners to hell, then it is pretty easy to see that she has posited traits that cannot coexist. Pointing this out may be an argument against her belief system, but not against theology in general.
Which argument intended to prove theology is the best? Well, none really. They’re all bullshit. Some are hypnotically idiotic, some are nonsense wrapped in science, some are just plain silly, and many are personal stories or anecdotes. But none I’ve encountered really stand out as a step closer to proving the supernatural.
