What is the meaning of "barnet front"?

In an article in yesterday's European, on the US election, Kevin O'Sullivan, writing of Hillary Clinton says,

In fairness, on the barnet front she's head and shoulders above her rival. But then, again, who isn't?

The text had previously just been referring to her lack of sartorial elegance, and then this mention. What is the barnet front?

Barnet is Cockney rhyming slang: Barnet Fair → hair.

On the X front is a set phrase relating to the particular situation of X:

2.3 A particular situation or sphere of operation:
‘there was some good news on the jobs front’
‘On the political front, the situation has been marked by total paralysis.’

ODO

Thus: "In the particular matter of coiffure, she's in a far better position than her rival."