From a Victoria's Secret addict:
Yes, the package will be obvious that it is from Victoria's Secret, the type of packing is different than most, and the logo is fairly visible on the package itself.
It terms of the catalog, if you're looking to get her a bra or underwear, then they will most likely carry it in the store and they can help you find it. They also have a great beauty (perfumes etc.) section that you can find many great gifts at in the majority of the stores. Also, it varies from location to location, of the three different stores that I go too, each one has more/less/different selection than the others. So just go, ask for help, and maybe you'll find what you're looking for. However, if you're looking to get her clothing, they do not carry that in the store, and you would have to order it online / on the phone.
If you have to get it from the catalog - is there a work address you could ship it to? A friend's house? I'm sure you can find ways to be sneaky about it. And I guarentee she will be <b>very</b> happy! Good luck!