> 
> ‘I did. But when I reached the telephone, he had grown tired of waiting and had rung off. I should never have allowed Miss Wickham to take me away from the house.’  
> 
>  ‘She wanted you to see the big fish.’  
> 
>  ‘So I understood her to say.’ 
> 
> 
> 

Can anyone help me with construction of the last sentence. Is it common in English?
I was expecting 'So I understood what she said.'