I went back and looked up the relevant passages from chapters 13 and 14 that might answer your questions. This is how I interpret the passages, I recommend going back and re-reading these chapters.
Mizriath wrote:It was said even Niami did not know the full truth about the Mi'shara. They are created by GoG for a specific purpose. And they will be free after their purpose is completed. Did Spyder knew about that? Did spyder had an offer for the same. She existed for about 10,000 years.
Chapter 13 wrote: “Yes, that’s a part of it,” he nodded. “But there’s another side to that, Tarrin. A mi’shara is born out of Entropy so they can break the rules, to correct a problem that demands that kind of attention. But the other side of that, Tarrin, is that the mi’shara is destined to adhere to that task. Son, you and your son, and Spyder, all of you are the only mortals born with a future laid out for you. No other mortals have that restriction. There’s no such thing as a future, after all,”
“That’s alright. Now then, when the Firestaff first arrived here, it was enough of a concern to bring about the first mi’shara, someone who died long ago,” he explained. “That mi’shara was tasked to hide it, keep it out of mischief.”
“Why not destroy it?”
“Because I don’t really like doing that unless the situation demands it,” he answered. “The Firestaff served a purpose, Tarrin. It was a part of the way things work. Yes, it destroyed worlds, but that destruction is sometimes necessary to foster creation. It’s part of the cycle of life, just on a much bigger scale. Now, the first mi’shara born to deal with the Firestaff did his job well, holding it through its first cycle. Then he hid it and passed on. But, he didn’t hide it well enough. Five thousand years later, Val found it and used it, and touched off the Blood War. Spyder was the mi’shara spawned because of that little incident. Her task was to fix the damage and get Sennadar back under control, and she did her job well. But, when its last cycle came about, Entropy spun you out, my son, and tasked you with dealing with the Firestaff once and for all. It had become too dangerous.”
“Hold on. You said there’s no such thing as the future. If that’s so, how does Entropy know to make mi’shara?”
“Ah, because sometimes, there are some events that become unavoidable, and the only way to avoid them is to create a mortal that exists outside the normal rules,” he said. “There is no future, Tarrin, but there is the possibility of the future. Entropy, as well as some gods and even some mortals, are very sensitive to those possibilities, and they can read them. Kikkalli, she is a good example, Tarrin. She is sensitive to the lines of probablity, and can predict future events with some accuracy. However, when all possibilities converge into a single path, then Entropy knows that something is wrong, and it reacts. In your case, all possibilities converged on a single event, my son, and that event was Val reclaiming the Firestaff and destroying your world. Entropy could not permit it, because it would start a chain reaction that would force the universe down a single path. That is Entropy’s true purpose, my son. Yes, it represents destruction, but its ultimate goal is to maintain randomness. Fire, as you might have noticed, has a similar reputation as a destructive force, but it’s also vital for survival. Entropy is like fire, just on a very grand scale.”
It's not the GoG that creates the mi'shara it's Entropy. And it's also mentioned here that Spyder's job was to help pick up the pieces after the blood war, but she had to end the blood war first. So I think that what happened was that after Spyder got everything put back together, more or less, the gods of Sennadar saw what good work she was doing or accomplished and tapped her to ensure that things didn't get out of hand again. So she got a new role as guardian and a therefor new purpose in her life.
Mizriath wrote:How come Spyder did not know about mother Wynn and the Arakite girl? This two was born after Spyder .... based on what Fel mentioned Mother Wynn a few thousand years while the Arakite girl was a few hundred years. Niami would have known the truth....
Chapter 14 wrote: Behind her came a gnarled old woman with long gray-white hair, wearing a simple peasant dress and a cloak, but the sinuous grace with which she move belied her elderly appearance. “Spyder, I’d like you to meet Mother Wynn,” Tarrin said. “She’s been my teacher for a while. She’s almost as strict as you.”
“I doubt that,” Spyder said with a smile. “A pleasure. It is nice to know the name that goes with the face.”
“So, you remember me, do you?” Mother Wynn asked with a cackle.
“I do not forget, madam. Ever,” she said simply. “It has been a few thousand years, but I remember you.”
Spyder obviously knows Mother Wynn but Sashi was born on a different world, she looks like an Arakite but she isn't from Sennadar, and has never met Spyder.
Chapter 14 wrote: She sighed, then nodded. He kissed her gently, and then accepted fond farewells from everyone, and then to everyone’s surprise, he got up and went out the front door, careful to close it behind him. Miranda gasped and ran to the door and opened it, not even half a second after it was closed, but Tarrin had vanished. There was no sense of him using Sorcery, no use of Druidic magic, no Wizard spell…he was just gone.
Miranda laughed. “He has to tell me how he did that when he gets home!”
“I think he’s learning too many tricks from Spyder,” Jasana noted to Triana.
“I think you’re about right, cub.”
If Tarrin left without using a gate I don't think it would be too much of stretch of imagination to think that Mother Wynn and Sashi wouldn't need to use a gate to enter Sennadar. So why should Niami know the truth? If they don't come through the gate neither the Elder Gods or Spyder would be aware of them.