The gift earns nothing back: it is described as a gift to the U.S. government, not an investment, and it is not refundable. Whether any Canadian tax treatment applies is a question for the dentist's accountant, not an immigration matter, and no deduction changes the immigration analysis.
A gift is a gift, on both sides of the border
Hypothetical example: the dentist's bookkeeper asks whether the payment could be run through the corporation and treated as a cost of expanding the practice to the United States. The immigration answer is narrow: the payment is a gift to the U.S. government plus a processing fee; it purchases no asset, commercial interest or guaranteed outcome and must not be modelled as an EB-5 investment.
If the professional corporation would be the payer, the dentist must not assume the payment will be treated as her individual gift, because the official program distinguishes a US$1 million individual gift from a US$2 million corporate-sponsored gift for an employee. Whether the corporation may sponsor its owner, whether its payment is a shareholder benefit, and whether anything is deductible require current official confirmation and Canadian tax advice. She should also allow for the other costs identified through the official process, including any State Department fees, medical examination and professional assistance.