How to send attachments to windows users properly

Under Edit > Attachments, check Always send Windows-friend attachments.

That way, the text beneath the attachment won't be cut off.

Alternatively, you can do that on a per-message basis in the attachment file selector window, like so:

There is no easy way to convert iWork documents to Office and then send them via email. In short, your options are as follows:

1. In Pages, don't save as .pages files, but rather as .docx files. To do this, your grandmother will have to use "save as" every time she saves the file, because "save" will simply save a .pages file. You cannot set the default file format in Pages to be a .docx file.
2. Continue as she is doing now, and convert each file individually from .pages to .docx when she needs to send it to someone.
3. Buy a legal copy of Office:Mac.

If your grandmother works with people who use Office, the best solution is for her to use Office:Mac. Pages can open Word documents, and it can save as a Word document as well, but this conversion is limited. If the documents have a lot of formatting, they are likely to lose the formatting in the conversion. If she receives Word documents with macros, she will not be able to use or modify the macros. Keynote to PowerPoint and Numbers to Excel have similar issues. We'll leave aside that it sounds like you have violated the EULA for iWork in associating someone else's Apple ID with your grandmother's new Mac.

"Send Windows-Friendly Attachments" does not convert files from one type to another, and you probably don't want Apple Mail (or any other application) performing such a conversion without telling you about it. It simply changes the encoding that it uses for sending the files via email.

There is no method to batch-convert files from Pages to Word. Pages' AppleScript and Automator dictionaries don't have commands for such a conversion.