Hi jimbo, unfortunately Windows Defender only works on Microsoft devices.
Are the unwanted intrusions coming to your wife's Apple email or to any other email she might be using. If so then email settings need altering.
If they are unwanted pop-ups when using the Safari browser then the 'block pop-ups setting' needs to be set at maximum level.
Unfortunately Apple 'block pop-up settings' are not very effective and I use a free app named 'Blockbear'. It has sat in my iPad for the last three years blocking pop-ups if any have tried. I have not looked at it lately but as far as I remember it just needs the web addresses of the offending sites put in it and it will block them forever.
Part of my iPad screen showing the Blockbear icon
View attachment 147206
It obviously looks at all sites you are viewing to check for pop-ups so it is nosy!
But Apple would not have it as an app if it was dodgy. All I can say is I've used it without any apparent problems