hi wondering if you could tell me what would be best puppy food for my new 7wk old chi

Hi..I'm new on here as well and actually I need a lot of help with my little Chihuahua who is 4 months old..I think she's mix with some kind of terrier but not sure what.
She barks a lot when alone which I'm sure she needs lots of attention and she like to nip a lot which I know it's normal since she's still a puppy but man, she has soooo much energy like an energizer bunny. During the day when we are gone she has to stay in her play pen which I know she hates. What else can I do to make her feel more comfortable while we are away?