I found out how to do this myself. I logged into SquareSpace, went to our website and copied the link to our Donate button posted there. In a separate browser window, I went to our Email and add a Button Section. When I clicked on that section on the left, a selection opened on the right that included a place to fill in a URL for the button. I pasted in the same URL there that we use in the website. While editing that draft of our email I was also able to create text inside the button that now says Donate. And, I was able to select the largest text size.
