Excellent, exactly what I needed.

OK, let's start with the "good" message (because it is simpler, no other reason). It has two parts: an HTML text and one attachment. Simple.

The "bad" message has also two parts, but each of them is nested. The first part has two sub-parts, the text in plain text and in HTML. (Does your phone show the text? And if so, in what format?) The second part is also nested, with three attachments: one JPEG and two PDFs. There is nothing inherently wrong with that format, a semi-decent email client should be able to process it. It looks like a bug the N9's client.

For completeness, it might be interesting to see the email after being forwarded by your wife. You say your phone can read that correctly, maybe her email client reformats it before sending to a form your phone can understand.