Ridloff was asked which superhero is faster in an interview with CineXpress (via YouTube). “Okay, so this is a conversation I had with my son,” Ridloff said. “When he first found out that I was going to be the fastest woman in the universe he said, ‘No you’re not.’ He brought over his laptop and looked into the computer and said, ‘Look! It’s true! Flash is faster than Makkari.’ But I’m sure [it’s] Makkari … because she travels faster than the speed of sound.”
More specifically, (puts on nerd glasses), Makkari is capable of traveling at up to Mach 3, which is three times faster than the speed of sound, according to Marvel.com.
So, does that make her faster than the Scarlet Speedster? It depends on which version of The Flash you’re talking about. The Barry Allen Flash from the Arrowverse is capable of topping out at Mach 3.3, making him a bit faster than the fastest Eternal (via The Take). With apologies to Ridloff, it appears her son has a point.
Until we get a Marvel-DC crossover movie, this debate’s going to remain hypothetical.