A very simple "plug and play" spinner could be one of the spinning icons from the Font Awesome Wpf Package (Spinning icons).
The usage is quite simple, just install the nuget package:
PM> Install-Package FontAwesome.WPF
Then add the reference to the namespace
xmlns:fa="http://schemas.fontawesome.io/icons/"
and use the ImageAwesome control. Set the Spin="True" property and select one of the "Spinner", "Refresh", "Cog" and "CircleOutlinedNotched" Icon. It's scalable and can be resized by setting width and height.
<Window x:Class="Example.FontAwesome.WPF.Single"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:fa="http://schemas.fontawesome.io/icons/"
Title="Single" Height="300" Width="300">
<Grid Margin="20">
<fa:ImageAwesome Icon="Refresh" Spin="True" Height="48" Width="48" />
</Grid>
</Window>