As long as Zerlina doesn't seem upset or stressed, and isn't coming out with injuries, I wouldn't worry. My too wrestle all the time, and when it was the new kitten, I used to worry about Mozart being rough, but now it seems like it's Mozart who gets chewed on the most.

Generally, cats are pretty good at drawing the line themselves. Just keep an eye on them, and make sure Zerlina isn't getting upset, injured, or bullied, and they should be fine.