I'll tell you too, that she is wrong. I've bought them before in smaller demoninations (I and EE bonds) but only recently in larger demoninations to earn frequent flyer miles. It's a purchase, not a cash advance. A cash advance is going to a bank and getting cash from a credit card, sticking it in an ATM and getting cash, or using a service such as Western Union's cash transfer service. All these transactions have the word "cash." Buying savings bonds is a purchase. Either for yourself, or as a gift (I have purchased bonds as gifts too). They're not cash, but an IOU from the Federal Government. You can't get cash them in for a minimum of six-months, anyway, so U.S. Savings Bonds don't even fall under the category of "cash."
Also, Series EE Bonds are now also called "Patriot Bonds." How patriotic would it be for a bank to charge you a cash advance fee, a higher interest rate, plus interest starting from the day of purchase until the day you pay it off, for you being patriotic for purchasing these things?