Wow, that is a hard question because it is so subjective.
I started with Android tablets but eventually moved to the iPad. The reason being is that the apps available for the IOS (iPad) at the time I made the switch which were much more abundant. That is not really the case anymore as most all apps available for the iPad are also available for the Android OS.
I would base the decision more on what you think she will do with the tablet. If she is just going to use the tablet for email and web surfing, they are both about the same. Although I will say that the iPad is a LITTLE less suspect able to trojans, malware and viruses, not much, but a little. The IOS operating system, I know that is redundant for all your geeks, is a little better protected in the actual architecture, but the Android OS is catching up.
Does she have an Apple computer? If she does stay with the iPad, it makes the communication between the two a little easier. You will not need a third party app. If she is working with a Windows computer they are both about the same. You will need a third party app to do any real file work on wither of the systems.
It really comes down to personal choice. Which one do you think is better?
By the way if cost is a factor. You can get much more bang for your buck with an Android system. They usually have a faster processor, more memory and bigger screens for a much reduced cost. But stay with a reliable vendor.
The Google Pixel is really good, can be difficult to find, Sony is a really good one, and one of my favorites is the Samsung, but I really like their products in general. Samsung just makes some really good products with good support.
Stay away from the off the wall brands. They tend to be unreliable and you will have a hard time getting any support if something were to go wrong. Also check to make certain whichever one you buy has a recovery system. Most of the good ones do but many of the cheaper ones will not. That can be critical if you were to get a virus or a malware infection on the tablet.
I hope this helps.
Let me know if you have any questions.