If you're still having trouble with Wellmax, here are some secrets I've learned from fighting her around 30 times. I made a bet of $17 (24 gems) with my P2P friend that I could get her before him. So far I've failed with my meta-ish ragtag team while he's sat back, calmly evolving his Ushi tested team to max levels and BBs, ^likeafucko . I haven't gotten any exp, zel, or karma since I stopped farming honor points 4 days ago.

My team/info (for reference): Level 113 (101 energy, just about perfect for trials)
All units max 6* SBB10

• Anima Matah (L) Sacred Jewel
  
• Guardian Elimo Guardian Cloak
  
• Anima Luther Medulla
  
• Breaker Luther Medulla
  
• Oracle Darvanshel Sacred Jewel
  
• Lord Darvanshel (L)(Friend) Legwand
  

So, the tips:

• The turns for which Juggernaut is paralyzed (from Luther's BB, for example) does NOT count toward where Maxwell starts.
  
• The double Destiny starts BEFORE 30%, contrary to what /u/anubs said here. From what I can tell using this, double Destiny starts around 40%.
  
• It is always, no matter where you are in the trial, better to be safe and use cures/fujins/guard then to risk it, lose a unit, and use revives.
  

Other minor tips include:

• Juggernaut and Abaddon both die slightly before their health bars are at 0. (not sure if common knowledge, haven't seen it yet)
  
• I use this counter. Once you click next turn once, it can triggered by tapping space bar. This is helps when counting by getting you into a rhythm. I find it helpful to hit next turn right after I attack.
  

That's just my 2 cents. Hopefully, someone is able to use some of it. :P

Edit: 2 bonus tips I remember as I try again futilely.

• First, I find the best time to jump into Maxwell is Turn 17, so you can attack twice with full SBBs, then thrice after Maxwell's wombo combo.
  
• Second, Maxwell seems to target the low unit more than she doesn't. This includes attacks right after Rune and Destiny.