My 7 month old Doberman is really smart but she can’t focus for any length of time. She gets plenty of exercise. Do you have any suggestions?

I have a 7 month old, female, Doberman puppy. We purchased her at 5 months from a breeder, so she has been in our home for approx. 2 mnths. She is smart and seems to train fairly easily as far as basic commands. My problem is getting her to focus for any length of time because she is extremely active and has a very high prey drive. Maybe i'm expecting too much too soon...?

I've just recently (in the last few days) begun to keep her leashed and at my side at all times when she is indoors. She is crated when we are not home and for meals twice a day, and I was crating her when she became too rambunctious in the house, but this only seemed to aggravate the problem. Plus, she would scream at the top of her lungs for hours, she knows when we are still in the house and won't quiet down. When we leave the house, she is quiet in the crate. She is given "play time" twice a day for at least 30 minutes, with a toy, tennis ball, frisbee, that we throw for her. Also, she gets to go out at least once a day to play with our other Doberman who is 2 yrs old, male, neutered,... and they run, play and chase each other all over our yard. So I don't think it's a lack of exercise.

Should I continue with the leash indoors and out, or crate more often? Or some other suggestion?...Thanks so much!
Meredith