Was your grandmother a foreign person and was the amount of the gift over $100,000? A Form 3520 is not supported by TurboTax. The form is an informational form only and the amount of the gift received is not reported on your federal tax return.
IRS Form 3520 - https://www.irs.gov/pub/irs-pdf/f3520.pdf
IRS Form 3520 instructions - https://www.irs.gov/pub/irs-pdf/i3520.pdf