Note: I am not asking for help with the training itself, just about the role play might have within the training process.

So I have a dog (nearly 3, Finnish Lapphund) whose training battle has always been overexcitement. We missed early socialization due to a giardia issue/vet's orders to keep her quarantined. We've done a lot of training with her since, and she's doing relatively well now. She's responsive and workable most of the time, no longer whining, barking, or crazy circle pulling. She just now occasionally goes from being a model citizen to having quick, abrupt moments of diving toward other dogs before hitting the end of the line, remembering she's leashed, and then immediately coming right back to be "perfect" again. We take group class, and she gives "polite" behavior even within a few feet of other dogs for long periods of time. At other times, a dog could be 30 feet away and we might still struggle for a quick moment. It's a toss up to predict when she's going to crack for a second.

now my question is, as we continue our on-leash training with her, is off-leash play out of the question? I've heard mixed information regarding whether or not this might make her see other dogs as even more exciting as a play opportunity, or if this could instead create opportunity that is conditionally unrestricted, and therefore less novel over time with practice. She'd clearly love a chance for a good friendly romp, so what do you think? Would this negatively impact her training?