Not in total.

Only additional overflowing chakra transfers to the next round.
Meaning this.

Turn 1: 20 Charka.
If Mabui grants 40 Charka + 20 = 60 Charka Turn 1.
The system itself grants 20 chakra, However, the gauge limit is 40.
Anything above 40 goes towards the next round. So 60 - 40(Gauge) = 20.
20 Chakra will carry over.

Every turn the chakra gained and the gauge goes up by 20.

The scenario that OP has written is explained easily.
20 Charka was carried over. Making the amount 60. Mabui uses her mystery granting an additional 40 chakra due to her passive proc.
60 Total - 20 (Mystery + 40 Passive = 80.
Once her standard comes around, she'll proc her passive again.
40 + 80 = Max Charka.

Once you understand the system, you can play around which characters Mabui will be a battery towards.
Hopefully that helps!

If you have any question, feel free to message me.