Christmas Tree Instead of a black tree lets go for dark blue or purple. You can make it easy on yourself by buying a tree with lights embedded into it already, or even one with fiber optic lights. If you buy extra lights too that okay, but make sure there's no more then 2 colors of lights on your dark colored tree. Solid colors would be best but any more then 2 would just look too messy.
Ornaments Ornaments can be glittered up sprays of silk flowers, items covered in rhinestones, skulls, roses, pirate ships. Certain animals have a Gothic Loli appeal such as owls, octopus, reptiles, skunks, certain insects like spiders, and natural colored butterfly. If you choose, you could theme it like Nightmare Before Christmas, Alice in Wonderland, or Pirate would all work well. The tree topper should be charming but still hold a Gothic appeal, a picture frame that looks like a cameo with whatever picture you like inside. Or maybe a Victorian doll doll dressed up for the occasion.
Stocking Stuffer Once again jewelry works well, try looking for gun metal colored items with an antique feel (even if they're not). Pearls often look lovely with gothic in colors such as cream, black, cranberry, and dark blue, try to find a color you know will match parts of her wardrobe. Fitted T-shirts in dark jewel tones can be worn with most black skirts when she's going casual, look for ones with covered necklines, and maybe puffed sleeves. Only buy one with a print if you KNOW she'll like it. Makeup can be bought, Aromaleigh is gone, but other amazing people are still out there working hard to fill the gap, Meow Cosmetics, Fyrinnae, and Geek Chic Cosmetics are just some of the places out there you can go you buy your Lolita makeup. Once again stick with dark jewel tones, blacks, or grays. Samples are best, if you want to pick up a full size try picking up a finishing powder and you don't have to worry as much about getting a color match wrong, maybe pay attention to whether she likes matte or sparkle makeup. Flowers might make a lovely gift, this time make them live potted flowers, a mini rose bush, orchids, or iris.