I went through the Miaphysite route, but I took a longer, harder path with more rewards.
1. Choose Intrigue Focus, choose any ambition except 'Groom Heir', maybe even leave it with no ambition.
2. Spy on your husband, he's trying to get you title and is not very good at hiding it, it won't take you long to find the proof.
3. Declare a Holy War on Jerusalem for Ascalon.
4. Give your heir some of your excess land, I gave him the whole Sinai in my case.
5. Go on a Hajj to Mecca. We're farming for Piety here, so choose the options that offer it, hopefully you get the Humble trait in the event chain.
6. Now comes the part where a lot of people have to die for your own benefit. Beat the weak Jerusalem army and divide your army in three to siege the three Ascalon provinces. By now the Pope has surely called a Crusade on you and everyone in Europe is gearing up preparing for it, you are on a timer and we need 250 piety
now. Charge the holdings with your armies to get 100% score.
7. With the Hajj plus Ascalon you should have 250 piety. Find some Miaphysite boytoy, the Armenians are more prone to like you because of the shared culture, but you are probably going to have to buy a favor to get them to come to you. Remember councilmen and people with important relatives won't come even with a favor.
8. Surely you have the evidence to imprison your husband by now. Go ahead and do it. If you succeed on the arrest that's great, if you don't, then you have to hurry up and win that war. Once you do. Execute your husband. Your vassals won't like it, but it's a quicker way to divorce and you'll get one count on the murder challenge.
9. Marry your boytoy, secretly convert to Miaphysite , then reveal it publicly. Crusade crisis averted.
10. Now take a look at your husband, he sucks, doesn't he? A lowborn is probably the best you could do and you're married patrilineally to him. He has to go. Divorce him or kill him, he has served his purpose.
11. Get a better husband that will accept a matrilineal marriage. There's a Bagrationi bastard around that could do the trick.
12. By now your depleted troops and outrageous behavior, surely has fanned the flames of factionalism. You will get a demand from a faction. Don't acquiesce. Yes, they probably outnumber you, but they are divided, you can beat them piecemeal by piecemeal.
13. The war was quite long in my case, but I won eventually. Execute those guys and complete the murder challenge.
14. Eveyone fears you, you are Miaphysite and in a matrilineal marriage with two challenges to go. Get the "Groom an heir" ambition and Family focus. Time to make some babies and lick your wounds.