Temporary Renter - agreement?

[Sarah Present]

We have a carriage house that we were planning to put on home away or other site similar for weekend rentals. However recently a neighbor though our neighborhood app was seeking a one bedroom rental for 3 months while her daughters family uses her home and looks for their own.  This seems like a nice arrangement - but is a lease of any kind in order?  I'm wondering if some type of month to month contract would be sufficient, or how extensive it would really need to be.

Thanks!

Sarah