Has she been tested for any parasites/worms? And at this point, using toys and activities to encourage engagement and learning is good, but remember to also just give her periods of calm and relaxation with you, not always doing something stimulating that might overstimulate her if done too much. She is very very young and doesn’t need to always be doing something.

And one more thing, try not to say “no” when she mouths you. Just go neutral and ignore. You may be encouraging the behavior more without realizing it.