Might be easier to restrict the older, settled cat to one room if the new one is stir crazy. Is there a section of the house your older cat prefers? I'd give it that area and restrict new cat from there, give it more time for each to feel that they are part of the same pack. Avoid them meeting as much as possible. With dogs, I do introductions. With cats, I let them have as much space for as long as possible, esp. to prevent potty issues.
It might be used to being outdoor or indoor/outdoor, you might try giving it some different litter or different scratching post or different things to do....but things that would be more pertaining to outdoor life. A bug to catch. A windowsill to observe birds from. An indoor plant she can eat. Litter that is more dirt-like. I see why you don't want to let her out, but perhaps short spells outdoors under your watchful eye? have a sunroom? leash?
Our three cats are rescues. One is too silly and scared to be allowed out. The other two would drive us crazy if we did not let them out. Stalking the door, scratching their way through screens in windows, etc. They are successful indoor outdoor cats however and I worry about them, but had to relent and let mine out. For you, however, in your situation, I'd still wait to let it out even if you plan to let it be outdoors later, just so it imprints on you and your house longer. I am a firm believer that indoor cats live longer but also feel cats can thrive in a variety of situations.
Bless you for taking her in....it sounds like we are kindred spirits.