Hissers are nocturnal so hopefully she's just sleeping during the day. Try checking on her at night time. They do come out during the day sometimes, especially when they don't feel threatened.
The images on those vendor pages appear to be what we have long called fusca, no matter what it is it is not giganteus. It is a big species but tiny compared to giganteus. Compare those images to the coloration of the real giganteus:
For me giganteus are easier than almost anything else. I feed them only dog food and haven't lost the culture in 30 years. Not productive enough for a decent feeder and only so many adults coexist but a great display creature.
Welcome! I'd suggest bigger containers for the isopods. Try vegetarian foods. You can get them far cheaper online but there is shipping cost and possible DOA. The zebra and dairy cows are probably among the best staples for trading.