Haha, yup, Morrigan and Flemeth lived in the Wilds together for most of Morrigan's life. Flemeth sent her out with the Hero of Ferelden to see the world before she was planned to come back and be taken by Flemeth, so she would be a more well-rounded individual (Morrigan wasn't aware this was the intention until further on in the journey, where her personal quests involve stealing Flemeth's grimoire which gave her the power to take Morrigan, etc. etc.). There's a lot of shit in Dragon Age
Yeah, I'm pretty sure she (he, now?) has transferred over to Solas' body and ditched the previous form. Which is weird. She normally only does that to her daughters; not sure if you spoke much with Morrigan (team member in DA:O, daughter to Flemeth), but she was slated to be the next transfer and rebelled against it, turning against Flemeth. Looks like Flemeth decided to honor Mythal's friendship and do her a solid by offing the Wolf
Solas is in between Tevinter and Nevarra, if you google up a map of Thedas. During my travels with Solas, he was constantly a source of theological debate and overall a very scholarly person, always up for a deep conversation. Whenever anything came up about elven lore and the gods, he (understandably) had a lot to say, and a lot of wisdom to impart. As I see it, the next part of the story has to involve Flemeth as a main piece. She is now the most powerful being on Thedas, she has absorbed multiple gods and their knowledge, and she's a fucking dragon witch for Christ's sake. Her actions have ranged from evil to good, so I'm not sure which way they will take her. She can no longer be neutral.
It's been a while, so I'm rusty on the lore, but Solas wasn't holding the Dread Wolf, the Dread Wolf was Solas (Solas is just the location he woke up in, and so he used it as his moniker), and Flemeth, acting on her friendship with Mythal, took his essence as punishment for his transgressions (screwing over all the old gods for fun). AFAIK, in the Dread Wolf's slumbers, he found out of Corypheus' awesome power and didn't know he was pure evil, just a power strong enough to free the gods; he was na´ve and took him on his word that he would help.
What exactly do you need to know? Flemeth has been in the trilogy since the first Dragon Age, so you probably don't know much about her, huh? And Mythal? Plus, without Solas in your party, you probably didn't hear much about his true identity before the grand reveal at the end, I assume.