Thanks for all your patience throughout this process and for sending us some more information via DM. We're going to respond here in the community so others may benefit from the information as well.
You asked about a Co-op Cycles REV20 6 Speed for your kiddo who is 5. Just to clarify, you're asking about the Co-op Cycles REV20 6 Speed Plus Kid's bike? My daughter has a similar inseam to your daughter's and she rides a Salsa Timberjack 20"+ (very similar in geometry to the REV20 Plus) with no trouble at all. The only concern I would call out is to make sure your kiddo can reach the brakes with her fingers before she goes ripping down those hills!
Best of luck, keep us posted on your cycling adventures!