This is uh, well, you’re asking for something. To put it plainly, websites can and should be dynamic, and they should be able to operate under a hundred different instances and still come out legible. That she is attempting to make the visual editor match the page exactly is not going to happen on anything other than her own personal machine and any other machine that matches those specifications. If she’s there trying to make exactly 5 specific lines of text line up to an inline photo exactly, that’s uh, something. It won’t be the same lines of text if the browser window shrinks and the page responds (and if the page doesn’t respond your website is badly made), it won’t be the same lines of text on mobile, and it won’t be the same lines of text on a different photograph that has different dimensions, or if you add italics, or basically anything. So she needs to stop trying or think of a different way to present the material. For example, if specific text has to be associated with a photograph, I’d recommend a caption that is tied to the photograph and will go wherever the photo goes.
If you force the div the text is inside on the webpage to be wider to match the visual editor using CSS, there is a nonzero chance it will cause a visual cascade failure on the website layout and the whole thing will break in new and interesting ways as divs go out of bounds of the wrapper dimensions. It’s possible the theme is constructed in a way that makes it possible, but it’s unlikely. Look through appearance customization options to see if there is anything that desginates the width of the main blog area - if there is any way to change it for a newbie without breaking the whole thing, it’s going to be there.