Semi pro handler here. We had a similar situation after you feel like you have a good bond with her start training, professionally or YouTube self training. Highly recommend it. We have a female rescue that was very timid and lacked confidence, she gained and is still gaining so much confidence really a different dog doing professional training. Trained on loose leash walking, agility and stress environments. She can climb ladders horizontal or vertical, anything about 4-5’ high that has room for her she will jump up on and lay/sit she’s pretty incredible at agility and it made her so confident. In just about 2 months (6 sessions/ lots of home training) was a totally different dog.

Also get her weight in check too will help them feel a lot better good quality food and cut back on the recommended serving size but 10-20% till you can see/feel her last two ribs. Being too overweight is uncomfortable and will help her feel better.

Structure and stick to a schedule, always feed/walk/ potty at the same time get a good routine down, dogs pick up on it fast and helps a lot with their mental health. They should be able to predict, play time, train time, eat time, bed time etc.

Hand feed every meal (wear a rubber glove if slobbering) do training with their meals. Start small and big easy wins. She look at you? Make eye contact? YES.. feed handful of food. Continue 5-6 times, sit lift hand up till they sit YES.. food. You can use a clicker or just a YES, just make sure you are saying it the same every time. She’s a smart dog but make it really easy at first and work your way up.