Personally I’d have waited, until the child would voice a wish to get rid of it, before starting to plan on doing something. Depending on the kid it could take a while.
Also, I remember Madonna’s daughter Lourdes sporting a unibrow (and a mo) until she was at least 11.
LEt kids be kids. Honestly i feel it is pathetic that we dump our insecurities on them so young!
poor child.
Quite recently i write in the AEA facebook group on parent’s projections and the resulting possibility to manipulate the children. And even if that girl wished to have her eyebrows waxed it would bei the responsibility to explain her daughter why she was too young.
I would rather look at my childhood photos and not see a unibrow (and you know that’s all anyone else can see, too). But maybe that’s just me 
So sad to hear! Let them have their childhood