There are a few ways we can tackle her shirt…
For me there is only one way which will ultimatly save time too. We already have the shirt geometry in the scene, so why start from scratch?

We have a basic model, but when you make your other models visible again you will see that the mesh intersects, or is hidden by Mandy.
A quick way to fix this is to select the vertices of the shirt and move them along their normals. This will scale them outwards, relative to each other rather than as a whole.
In Maya you can select this under the Move Tool attibutes, in Silo just select Local Move.
There we have the basic shirt model, so next we can start to add some details.