It's illegal to buy a handgun as a gift anywhere in the US. Buying a handgun as a gift is considered a straw purchase. She just needs to give you the cash or a gift certificate. Then you can walk into the store and make a legal purchase.
Based on the ATF documentation it is not illegal and is not considered a straw purchase.
If you are legally allowed to purchase a gun and the person you are purchasing is legally allowed to own that it's not straw purchase. Basically if the person you are purchasing it for could purchase it them self without problems then it's ok.
The issue comes into how the Federal law is worded. It doesn't not indicate any of this.
See:
Straw purchase - Wikipedia, the free encyclopedia
In the context of United States federal gun laws, a straw purchase is defined as any purchase from a dealer holding a Federal Firearms License where the buyer conducting the transaction is acting as a proxy for another person. The law does not distinguish between someone who is purchasing on behalf of a person who legally cannot purchase or possess a firearm, and one who is not.
In the United States, straw purchases are a felony violation of the Gun Control Act of 1968 for both the straw purchaser (who can also be charged with lying on Federal Form 4473) and the ultimate possessor. One of the questions on Form 4473 is “I am the buyer of this firearm” and the purchaser must answer honestly yes or no, by checking the appropriate box in ink. However, purchase of a firearm as a bona fide gift for someone who can legally own such a firearm is permitted.
http://www.atf.gov/publications/download/p/atf-p-5300-4.pdf
15. STRAW PURCHASES
In some instances, a straw purchaser is used because the actual purchaser is prohibited from acquiring the firearm. That is to say, the actual purchaser is a felon or is within one of the other prohibited categories of persons who may not lawfully acquire firearms or is a resident of a State other than that in which the licensee's business premises is located. Because of his or her disability, the person uses a straw purchaser who is not prohibited from purchasing a firearm from the licensee. In other instances, neither the straw purchaser nor the actual purchaser is prohibited from acquiring the firearm. In both instances, the straw purchaser violates Federal law by making false statements on Form 4473 to the licensee with respect to the identity of the actual purchaser of the firearm, as well as the actual purchaser's residence address and date of birth. The actual purchaser who utilized the straw purchaser to acquire a firearm has unlawfully aided and abetted or caused the making of the false statements. The licensee selling the firearm under these circumstances also violates Federal law if the licensee is aware of the false statements on the form. It is immaterial that the actual purchaser and the straw purchaser are residents of the State in which the licensee's business premises is located, are not prohibited from receiving or possessing firearms, and could have lawfully purchased firearms from the licensee.
However further down their example shows that purchasing a gun as a gift for someone is not considered a straw purchase.
An example of an illegal straw purchase is as follows: Mr. Smith asks Mr. Jones to purchase a firearm for Mr. Smith. Mr. Smith gives Mr. Jones the money for the firearm. If Mr. Jones fills out Form 4473, he violates the law by falsely stating that he is the actual buyer of the firearm. Mr. Smith also violates the law because he has unlawfully aided and abetted or caused the making of false statements on the form. Where a person purchases a firearm with the intent of making a gift of the firearm to another person, the person making the purchase is indeed the true purchaser. There is no straw purchaser in these instances. In the above example, if Mr. Jones had bought a firearm with his own money to give to Mr. Smith as a birthday present, Mr. Jones could lawfully have completed Form 4473.
The use of gift certificates would also not fall within the category of straw purchases. The person redeeming the gift certificate would be the actual purchaser of the firearm and would be properly reflected as such in the dealer's records.