With Margaret, getting the numbers is very tricky, because it requires raiding to get the specials fired at my heroes at certain time, but I managed to get some screenshots to establish some facts:
Here’s the screenshot of single mana gain after dodge with no mana bonus (look at Margaret’s mana):
After that, I played with my regular mono team, which has mana troops and mana spirit link bonus:
Here are numbers after Evelyn and Margaret dodged (no spirit link bonus, just lvl 11 mana troops):
And here’s when Telluria dodged with lvl 17 mana troops and spirit link bonus (it expired after she dodged):
So it looks like Margaret’s dodge bonus is flat 24% (23.8 ~ 24.2) regardless of hero’s mana speed, but it is affected by mana bonuses from troops and skills.