is zyra is a good mid laner?

Balanced, I personally think she is better as a support because of her zoning, but that's just me

Zyra is fine as a mid lane but she's much better as a support.

She's a fine midlaner, very strong, good utility.

The downside to her is that she's VERY squishy and easily ganked.

Really susceptible to burst assassins and junglers that can get around her e (Lee, Elise, Shaco et al). Fine/very strong against traditional mages and junglers that close in a predictable manner.