statusstrip label text

There are a couple of ways to address this, but the easiest is to make the statusstrip in the form public.

You can use the delegate, but more correctly are using interfaces.
For example:

public interface IMessenger
{
    void ShowMessage(string text);
}

And inherit maybe main form, or maybe other classes from this interface.
In the appropriate classes/forms make for example a property 'Messenger', set it and use. This way is more flexible than delegates.