I don't think we even started classes until Loki was around 5 months old. We had to find a good trainer and then wait for her next round of puppy classes to start. We've been doing it for over a year now because it's so much fun.
I'm glad that you realize you have to work with them every day. Loki and I do "homework" every day for anywhere from 15-60 mins. We work on leash walking on our daily walk. I ask him to sit before he goes outside, before I feed him, etc. Even though he knows all of these things, we practice. Besides, he has learned what he needs to do to get what he wants. No begging at the table, but if he lies down and looks sad for 10 mins chances are i'll put a little tidbit in his bowl when we're done! They are so smart! You have to give her another chance