I am no expert Kirsty,
but I do not think that you are going to fix this in the visual editor. It appears that some code is inserted in the page that is not quite standard.
It may be that the developer has set this up so that those images or the code that surrounds them is added with some PHP wizadry but I suspect it has been hand coded in the text editor for that page.
If you look at the source of the page in your browser, about half way down the page, you should be able to recognise where the images and text are. The images that are aligned correctly are contained in a div with a specific class, like this:
<div class="asso-img"> and it is the class that assigns the style that lines everything up neatly. The image that is misbehaving isn't in a div like that and there are one or two other things that make the code look a bit sloppy.
You can tell if it is hand coded in the page by looking at the text view in the editor. If it is full of that code stuff then that is how it is put together. If not, then I am as stuck as you are!
Whoever built the site could probably sort this within ten-minutes.