What is Tess’s mother’s response when she hears about the sexual encounter between Tess and Alec?

Are you referring to the section in which Tess tells her mother about her pregnancy? If so, her mother, Joan, tells her that they must make the best of it....

‘I thought if I spoke of his fond feelings and what they might lead to, you would be hontish wi’ him and lose your chance,’ she murmured, wiping her eyes with her apron. ‘Well, we must make the best of it, I suppose. ‘Tis nater, after all, and what do please God!’