6 month old puppy with BIG bark

We just brought home our 6 month old pitty mix puppy Poppy from the shelter 2 days ago. Shes getting along really well with our 5 year old female pitty mix Olive, and vice versa. She is so sweet, very gentle, chill for a puppy and a fast learner.

She does, however, have a very loud and intimidating bark. She barks at our cats, barks at other dogs/people while we’re walking, barks at kids, barks at her own reflection in the mirror, barks at things out the window, etc. we live in an apartment building with lots of other dogs so this is becoming very inconvenient and stressful for neighbor dogs. Once she meets the dogs/people she is silent, playful, gentle and sweet, not bothering adult dogs who aren’t into playing etc.

I’m hoping to get some advice on how to combat the barking, especially on walks and with the cats. As of now I get her attention if I can, make her sit and reward her when she is sitting and quiet. We plan to socialize her often at our local dog park and with our friends/families dogs, but I would love any insight from those of you who have overcome this!