If the dog is housetrained then it's not likely to be a problem. Immediate clean up of any accident should be sufficient to prevent an odor. You might want to give the guest access to appropriate cleaning supplies that you want to have used on the floor if this occurs. A couple of old towels for the big mop up, and then paper towels and a cleaning product for the final cleaning.
If you are really really worried you could ask the guest to keep the dog on a leash inside the space (this keeps the dog within a few feet of the owner for close observation but is not relaxing or convenient for the owner) and/or put her in a crate/kennel when indoors. However, it would be best to ask this before the reservation was made since some dogs are not crate trained and although perfectly well trained in other ways become stressed or claustrophobic in a crate.
We have lots of dog visitors and no issues. We do NOT ever allow the dog to be left unattended in our property unless the dog is crate trained and the owner puts the dog in a crate when they leave.