If you're going to read books and do email and surf a little, any of them will do.
Yes, your iPad will bring more money when you decide to swap, but the apps are only available on iTunes, which is ok if you swap to another Apple product. Some apps can be shared with your smartphone if you have an iPhone.
Windows is fine and has tons of apps and she's probably already familiar with it.
I have an Android smartphone and Windows on my computers. They can't share apps, but I use them for different things.
If I were going to do just the above, I'd buy a Kindle Fire. It's Android based and they have their own app store you can use your Amazon account with.
{My credentials? In the computer biz since 1985, starting with Commodore 64. Master's degree in Computer Information Science.)
And it IS true that you don't have to get malware on a Window's system. It DOES depend on where you go on the Internet and what links you click and what you sign up for with your GOOD email address. You DO have a temp account that you can use for newsletters, etc, right? :)
Just my 2c worth...
Norma