"The evening ended with dancing. On its being proposed, Anne offered her services, as usual; and though her eyes would sometimes fill with tears as she sat at the instrument, she was extremely glad to be employed, and desired nothing in return but to be unobserved."

So not only is she alone, but it's almost sadder that she's so unhappy that she actually wants to be alone and unobserved. We see this again as they head back from their walk in Ch. 10:

Her spirits wanted the solitude and silence which only numbers could give.

Here, not only does she seek out solitude, which is not surprising at this point, but she knows that everyone will ignore her if there's a crowd.