View|Headers|Normal should turn this off. I think yours is set to "All".

the extras I get are all computer jargon

But did you find that setting? Was it set to "All"? Did you change it to "Normal"?

It has been normal all the time

OK, can you please copy and paste some of this stuff?

Zelos thanks for the help. Just trying to help my parents out and not being familiar with T-bird I'm at a bit of a loss.

Here's a screenshot of what I receive from a simple text email from her.

http://i.imgur.com/xL5ZF58.png

Basically all I see is a bunch of HTML code. Can't find a setting that makes sense. Somehow their View / Message body as / was turned to plain text.

Fixed that so her incoming emails look normal, but outgoing (even after a restart still show the HTML code around everything,

What device is this on? It's too "zoomed in" to get the context. I'm not altogether sure that is Thunderbird we're looking at and some of the icons look like those I see in Android. Is it Windows 10? That uses some unfamiliar (to me) icons.

It is not a "simple text message" - it's using HTML markup and possibly is being viewed in a reader that doesn't support HTML. There is a checkbox in Account Settings in Thunderbird that governs whether or not messages are composed using HTML. It might be useful to set that to "off" on mum's Thunderbird.