I wouldn't worry about the visualizing too much. Lanie herself said she's not very visual. All you need is a "sense" of the person. Even if it is just a blurred shadow, but inside you feel it is "her", then it will work.

The problem you must deal with is the feeling that it didn't work. Hey, none of us are doing it perfectly, I'm sure - but it still works! So put that out of your mind. I have even experimented with people a few times (usually getting them to say non romantic things - but on an ex who tried to come back, I got him to say romantic stuff for a  short while), and because I didn't give a damn, I did the vis in a very rushed, haphazard manner. And all the exact words still came out). So don't worry and just do it. 

Are you lying down and relaxing? Do you get into a "state akin to sleep" that Neville Goddard talks about? i.e. almost asleep but still conscious, this is our most powerful state to visualise. 

Also, take some notes before you start doing PW about the person. Write down some of their characteristics, and things about their appearance. e.g. whats their hair like? What clothes do they like to wear? What do they smell like? What does their voice sound like? Are there any mannerisms that they always do? 

Hope this can help a little to amp up the visualising!