I believe that is the “Lady of Shalott” rather than the Lady of the Lake. She is sitting on the tapestry which she made because she couldn’t leave her room or look out the window. She had to look at life through a mirror. Interesting tale and story. This is the last painting of her before she is found dead in the boat Sir Lancelot.
...But Lancelot mused a little space;
He said, “She has a lovely face;
God in his mercy lend her grace,
The Lady of Shalott.”