Personally, I've never taken basic obedience classes, and we actually started Agility Foundation classes when Ivy was 6 months. By that time, she'd mastered the basic 5 with distractions. So I think how often you can practice the training is more important than how many classes you take.

Since you've already gone through one round of classes and know where your weak spots are (generalizing the behavior/practicing in distractive places), I say pass this upcoming class and take the opportunity to train Ginger consistently, constantly, and anywhere and everywhere you possibly can. Also, she is very young! 5 minutes of practice around the house and your town will produce a well-polished pup in a matter of weeks.

ETA: If you ever need help with training, too, you know we're all here to help

(P.S. For "Focus", try Doggie Zen. Once your pup understands that eye contact = treats and work, you can then use eye contact as a default behavior, like Sit.)