Does the moisture a woman sees after waking from sleep, which might be from the effects of Istinja' (washing after relieving oneself), necessitate ghusl if there is no fluid or smell of الاحتلام (nocturnal emission)?

The remedy for waswasah (whispers of Satan/obsessive thoughts) is to ignore it and not pay attention to it. If you doubt having had a wet dream, the default assumption is that it did not occur, and you are not required to perform ghusl (definition) (ritual bath) until you are certain that something necessitating it has exited. Each time waswasah is addressed, it reappears in another form. Its remedy is to cut it off at its roots and ignore it in whatever form it appears. Sheikh Al-Islam Ibn Taymiyyah said: "Indeed, waswasah is removed by seeking refuge [in Allah] and rejecting doubts. So, if waswasah comes and says, 'You did not wash your face,' then say, 'Yes, I did wash my face.' And if it occurs to you that you did not make an intention or say takbir, then say with your heart, 'Yes, I did make an intention and say takbir.' Steadfastness upon truth repels waswasah, otherwise, whenever Satan sees your responsiveness to doubts, he will increase them until he destroys you."