Hello,
I am at best an average player and just did God Queen without any of the spec defining Legos (I used prydaz and the vigour ring).
I have some tips that will hopefully help anyone still struggling with this challenge.
1. Focus sigryn and use a @Focus blind macro whenever she starts her channel
2. Don't DPS sigryn much at all to begin with, any bleeds and poison ticks will break your blind and cause a wipe. I mostly ignored her and focused on the jarl and the caster guy until she stopped doing the cast (which is around the time the jarl dies)
3. Priority for me when mechanics overlap was sig blind>runes>bubble caster. The caster has a slow cast time and the bubble is easy to break at around 920 ilevel so you have plenty of time to deal with other more pressing mechanics before popping and kicking him.
4. Use drums after the jarl dies and just focus sigryn only switching to pop the bubble and interrupt, the caster guy didn't need to die you just get Sig low enough and she starts the RP ending regardless of the state of the adds. I also feel like his Bubble gets progressively harder to pop which acts as a soft enrage so just focus the God Queen down.
5. I suck at this game. If I can do it anyone can
6. Remember to /focus Sig after every wipe, it clears your focus when you leave the instance and I wiped about ten times because I was spamming my macro wondering why it wasn't working only to realise she wasn't focused (see 5 above)
That's it, I found this harder than Agatha, but then I had much better outlaw gear as that is my main spec. The only real problem should be when mechanics overlap and you have to decide what order to do things in. Good luck!