I don't blame you--I would be soooooo in love with her if I were you!! I simply adore that photo of the two of you "screaming" at the camera!!! You should frame it.
I've never been any good at training. I declare I don't know how Lulu has learned all she knows. lol I will say, though, I do use a harness while walking so she never has pressure on her throat. The harness you posted a pic of looks fine. I also like one called a Buddy Belt in the summer as it's very strappy so she wouldn't get hot.
Here are a couple of pics of Lulu with a Buddy Belt on.