Yes she is a big head.
For a base wig I recommend this one in Ask Blonde.
First you need to fit the wig to your head.
Then you need to stub the wig
Then you make your gaint ponytal out of foam carve to the shape you need. Then cover it with wig fiber.
Here an example of one but in your case you want to glue all the hair down with Tacky Glue.
You might need to spike your stubs with a headband with dowel to support the weight of those ponytails as well underneath the wig.
I had to do this with Kongiku as her hair loop was heavy.