Hi Laurie,
I guess this isn't exactly what you are looking for, but it might work.
You can set an assignment whereby the students prepare their mind maps using whatever they want - Google Drive, Lucidchart, and so on - and then they submit the link, or embed it in a document.
You could also use the workshop activity which would allow other students to mark and comment on the charts.
As I said, it's not a complete solution but it may cover your needs.
All the best
Andy