I was also told that I must have a letter from the donor (my aunt) stating that my gift was pre-taxed money or I will have to pay the taxes.
The receiver of a gift never pays taxes on the gifted amount no matter how much it is. Now it sounds like you are trying to buy a home and the underwriter wants the gift to be in writing ... ask them if you have any further questions.
Now your aunt will need to file a gift tax return since she exceeded the $14K per year limit to any one person.
No, that's not true.
As Critter#2 indicates, if the mortgage company is asking questions, you need to address their concerns (usually that it's really a gift and not a loan). But, it's not taxable to you.