Liz is good with meter but she is also good at building it. Generally, she's a self-sufficient character.
As for the triple DP combo, it's explained in the first few pages. It's C DP, then A DP twice. There is a delay after the first DP that can be timed using a whiff cancel s.B, though it's not necessary. Basically, you want the 2nd DP to hit the opponent at the lowest point, right before they touch the ground.