A first meeting between dog and rabbit is best done with the rabbit inside a carrier. The carriers with the plastic sides so the bunny can feel somewhat safe. Put the carrier with the rabbit inside on the ground to let the dog sniff around it. Depending on your dog’s obedience training this can go very well, or not so well. A very excited dog is extremely frightening to a rabbit. If your dog goes all nuts over the bunny in the carrier, you will know you have to proceed very slowly, do many introductory sessions before the dog can actually have a face-to-face meeting with the rabbit. Don’t do this carrier-intro in Spookie’s space, where he lives, as this will only add insult to injury (figuratively speaking). Rabbits do not approve of other animals in their territory.
If your dog is very well-trained, as you mention she is a therapy dog, and knows her commands reliably, you might have a good introduction.
It is a good idea to leash Chelsea to correct her while she investigates the rabbit in the carrier. If she is calm and controlled, you can hold Spookie while she meeets him but you need another person to help you with this in case Chelsea does go nuts over the rabbit.