VPN suddenly appeared to her right hand corner of my iPadU

MS Defender installs a local proxy. Without delving into the technicalities, all local network traffic is routed via the local proxy installed on the iPad - where the traffic can be filtered/examined by Defender.

Due to the iOS/iPadOS system architecture, this proxy employs a VPN - even though a VPN connection is unlikely to be active. In this instance, the VPN "flag" is misleading. In the distant past, Apple allowed the VPN flag to be suppressed (i.e. hidden) - however, the ability of App Developers to do so has been lost in more recent OS versions, presumably to avoid the situation whereby network traffic could be "silently" redirected to an external proxy or VPN Gateway.

The one you see for Microsoft Defender is the one installed and why you are seeing it on your screen.

The button that says to Sign In to Work or School Account is on everyone's device and does not mean you have any VPN installed for that purpose. The VPN that shows connected on that page is Microsoft Defender.

Microsoft Defender is an app that you can download from the App Store that contains a VPN and you can remove that app if you had it installed. If you cannot find the app on one of your Home Screens, then swipe left all the way to the App Library and search for it there.

Many "security" Apps (e.g. Norton, McAfee etc.) install a local proxy through using VPN profile - even through a VPN (Virtual Private Network) connection may not be in active use on the iPad (or iPhone).

Similarly, if your iPad is owned by a business or an enterprise, the iPad may be centrally managed - and in certain circumstances, all network traffic might be routed via a VPN connection to the associated organisation's network.

With a better understanding of the ownership of the iPad - and the circumstances in which the VPN flag appears - contributors here might be better able to offer appropriate information or guidance.

I assume you have checked for a profile at Settings > General > VPN & Device Management, but that has not been made clear from your post.

Looks like it could be a bug if you are not running any software that is a VPN.