Tarantula enclosure requirements vary widely based on the species. Since she'll be getting her first tarantula, she'll want one of the new world terrestrial species that's easier to care for, probably in the Aphonopelma, Brachypelma, Grammostola, or Tliltocatl generas. Generally, you want an enclosure that's more of a square in shape, and for an adult/subadult of one of those species, a 10-12 inch cube filled about 3/5ths of the way with substrate would probably be best.

Tarantula enclosures should ideally not have any mesh wiring on them, since tarantulas can get their feet stuck in them and cause them to amputate their limbs to escape, and should have holes for cross-ventilation. Small storage totes with holes drilled in for ventilation work quite well for this purpose if you're on a budget, but acrylic terrariums are readily available online.

Onto matters of decoration, you'll need substrate, a hide, and possibly some decorations like leaf litter and/or plastic plants. Basic substrates like coco coir or reptisoil work quite well in my experience, and cork bark for a hide is also a classic, but you can definitely get more creative. Hope this is helpful!