I'll bet that one of the attorney types that follow this forum from time to time would LOVE to have a case in the US of Wolfster's GF being denied the use of a calculator if her condition can be documented. In the US there is a whole section of law that revolves around and covers persons with disabilities. If the use of a simple calculator, no phone, no camera, no poker related software of any kind, etc., as Nick said was denied, the casino, cardroom is opening themselves up to a serious lawsuit, which they will very likely lose.
What is different about her situation than the blind player who is allowed to have another person next to him who 'reads' his hole cards and the board cards and tells him the value and suit?
If she has a documented disability and brings 'proof' of that disability to the casino, the casino has a legal obligation to make all 'reasonable accommodations' to allow her to compete as though she had no such disability.
The proper action for the casino is to verify the existence of the disability and if she brings a calculator, to verify the device falls within the allowable limits. If so, then the floor and/or dealer should announce that she will be allowed to play with the device. They DO NOT have to say why, in fact, it may be a violation of the ADA to explain the why.
Hope this helps!!