A cat's normal gestation period is about 60 to 65 days, give or take. If you believe Jade is about 30 days into her pregnancy, then it may be another month or so, give or take, before she delivers.
If you haven't already, start feeding her a good, high-quality kitten food in both wet and dry formulas. You have probably already noticed that she wants to eat more than normal. Let her have as much as she wants, but don't overfeed.
Closer to her anticipated delivery time, Jade may seek out warm, dark, out of the way places in your home and choose one as her birthing nest. If you haven't already, it is time to provide her with a suitable nest for her delivery - keep in mind when choosing what is suitable as a nest that she will, for the most part, be in there 24/7 for the first 3 to 4 weeks of the kittens' lives. Whatever you choose should be large enough to accommodate Jade so that she can freely stand, turn, lay down comfortably. A large cardboard box is fine, others have used a large plastic storage tote. I use an extra-large dog crate. If you use a cardboard box, cut an opening for Jade to come and go but make it high enough so that the babies can't get out until it is time for them to. Line the bottom of whatever you choose with newspapers (a recently suggested good idea is to place the newspapers in old pillow slips) and soft old sheets or blankets. I also use old towels but as someone mentioned in another thread, the loops on the terry cloth may catch little claws - I have never had a problem with this, but I can see where it might present a concern. Once you have made a soft, warm nest for Jade, place it in a quiet room away from the normal traffic routines of your home and cover it with a thick blanket so that the opening you've made is only partially covered. Show Jade the nest and allow her to explore it at will. Hopefully, she will take right to it and have her babies in there when the time comes. You might even think about setting up a couple of different nests in different places - just think warm and dimly-lit.