Puppy Training ( Great Dane)

So I just got a puppy about two weeks ago and she’s from the All Pets Club. At first she seemed like the perfect puppy, very calm and a little skittish. The guy at the club told me she’s not very playful and kinda keeps to herself.

I fell in love with her and decided to get her the very next day. She my first puppy so I am kinda new to this whole Dog thing. (I have a maincoon) so I’ve noticed that she is afraid of doorways and cars and has had a hard time going on the pee pad she misses a lot of the time. I’ve tried to tell her she’s okay and that everything is fine but she hides and started to bite my cats tree house and we have had to remove everything around her because she gets destructive when we aren’t home. She also like to eat the cat shit so we have moved it to a location where she can’t reach it. It’s been a tuff time to be honest, I feel she understands and still does things that she isn’t supposed too. She is easily offended and cowers when we got to pet her and then once we pet her she will let us and be fine but I need help on how to help her and how to make her stop destroying things and not to be so skittish. Please don’t judge I am really trying to make it work.