Nope. Not in the calendars I can find, anyway. That’s not surprising, since “Brandy” is a name of recent vintage (heh), and refers to the alcoholic beverage. (The word “brandy” comes from “brandywine,” a transliteration of the Dutch “brandewijn,” which is literally “burnt wine.” The drink dates back only to the 1600’s or so.)*
If you are already named Brandy, or you are naming your kid after her godmother, etc., it’s not really anything that you can’t use. The Catholic Church is pretty relaxed about baptismal names, these days, as long as they aren’t actually anti-Christian.
That said… there are some very similar names that are older, and which would allow you to use Brandy as a nickname.
“Brand” is one of the Germanic words for “sword,” and there are a lot of names using that as an element. Most are male or have become surnames (“Hildebrand,” for example, which means “sword hilt”). But you can either ignore that or pick a feminine form. “Branda” or “Brandelina” would be the simplest female version, but “Branniardis” and similar forms are also pretty.
The Irish name “Brendan” can also be spelled “Brandon”, “Brandan,” etc. In fact, a lot of old medieval Germanic folks did have the name Brandanus or Brandan, after the saint.
What kind of patron saints do we have?
The most famous would be the Sts. Brendan. There’s also St. Maria Cristina Brando, who founded an Italian order of nuns when she was unable to join an existing one; and the famous martyr, Bl. Titus Brandsma. (And if you really have to, there’s the magnificently named Bl. Bramidanula of Marckdorff, a virgin of pure life.)
* Tolkien makes a linguistic joke in Lord of the Rings. Apparently amused by the American placename of Brandywine Creek (and the important Battle of Brandywine), he put a Brandywine River in the Shire. This name was a worn down version of its original name, the Baranduin (golden-brown long river).