LOL - welcome to the "terrible twos" as it's often known, or pre-adolescent phase. This is a stage that most boxers go through, and its going to test both your patience and your training ability (or dedication). It is something very much worth your while to dedicate time and effort to though - your well-behaved pet *will* re-emerge from this phase if you put in the required effort to guide her. If you're feeling optimistic, you could think of it as good training for when your own child reaches a similar stage of development
You've taken on a big task with a puppy to raise and educate into a well balanced dog - at the same time as having a human baby on the way (and now a newborn). It is a BIG ask, which is a major reason that most people would not recommend getting a puppy at that time, but instead waiting a few years. But at the same time, it's not impossible to do successfully - it's just that it's a big ask. The baby is, I'm sure, taking up every waking moment you have... but the puppy still needs a lot of time and dedication to training as well. Hard to do both at once - but that is actually the way out of your dillema.
How much help do you have with the dog? That is, is there anyone else who can spend some time on her? I ask this because - from what you have written above - it would seem that the major problem you have is a bored and idle puppy, who's finding ways of amusing herself that aren't exactly those you'd like. In reality, a puppy of this age should be out being socialised and exercised (good hard running & playing exercise, not walks) for at least a couple of hours daily. And on top of that, she *needs* mental stimulation. If she doesn't get it, then she's going to invent her own mischief - which is what I think is happening here. So ideally, you'd be looking at someone taking her out for some good hard exercise (playing at the dog park, or being sent to doggy daycare) for a good couple of hours every day. AND someone taking her to group training classes at least a couple of times each week. On top of that lot, some mental stimulation at home would also be very helpful - a little bit of training, but mainly the sorts of games that make her use her brain (for example, hide and seek - or better yet, hide and fetch where she has to find items you've hidden and bring them back to you).
The point being that this is an age where dogs start to think for themselves - they test boundaries, and they need their mental & physical requirements satisfied. And if they don't get it, they try to create it for themselves - usually in ways you'd rather they didn't. As is so often said, a tired boxer is a good boxer. That is absolutely true, and never more so when the boxer is an adolescent. But tired means both mentally and physically
Soo- I'm not sure how practical that is for your situation just now. I don't imagine that it is especially feasible for you
personally to be devoting that sort of time to your puppy when you have a newborn in the house. But at the same time, *someone* has to if the dog is to have the sort of guidance and education that is so vital at this age - and that is necessary to produce a well rounded and reliable adult dog. Is there someone else who can take on some of the training and exercise for you? If not, can you consider things like doggy daycare and paying someone reliable to take her to group training classes?
Btw: I see you have another thread about her barking at your newborn and running off with toys, etc. I won't reply in that thread also - but I would believe the problem (boredom) and solution to be the same as above.