Ah, Chloe sounds exactly like an Ivy.

Don't worry. Reactivity is actually very common, especially in high energy breeds. It's sort of "the dog who wanted to love too much".

You can join obedience classes, but I guarantee you they won't help as much than if you went directly to a behaviorist who is VERY experienced in leash reactivity (and preferably has dealt with these problems in his/her own dogs).

I highly recommend Leslie McDevitt's book Control Unleashed. You may want to read this before you set out on a search for a behaviorist. Many trainers/behaviorist like to command for 100% focus in the presence of other dogs, but, if you read CU, you will realize that that can even exacerbate the frustration and reactivity. She suggests using the game Look at That! which is explained in the book. I've experienced the vast difference between the two methods of dealing with reactivity, and I have to pledge my allegiance to CU. I actually have a couple videos of various dogs demonstrating LAT. If interested, just PM me! Leslie also addresses dogs who go bonkers with frustration even in crates and kennels and how to rehab that.

ETA: Re: bombproof dogs. Do you know anybody who has a greyhound? Greys are notorious for their gentle disposition. Most greys are 'bombproof' in the sense that they usually are not reactive. Or do you know anybody who has a very submissive/completely non-aggressive dog? Basically, any non-reactive, not-too-hyper dog would do. You just need them as a trigger.