Answer:
Guenevere knows Lancelot and is likely to disapprove.
Explanation:
At first, Vivien is surprised that Guenevere doesn't know yet, and she seems to think that it's for the best. She believes that Guenevere will disaprove, which can be clearly seen in the last line of the Dialogue:
<em><u /></em>
<em><u>Guenevere:</u></em><em> Well, for heaven's sake, who is it?
</em>
<em><u>Vivien:</u></em><em> Is it possible that it's not being gossiped </em>
<em>about? You really haven't heard? </em>
<em><u>Guenevere:</u></em><em> Not a syllable.
</em>
<em><u>Vivien:</u></em><em> Then I shan't tell you. </em>
<u><em>Guenevere:</em></u><em> But — why? </em>
<u><em>Vivien:</em></u><em> Because you'll think I've a nerve to want </em>
<em>him. </em>
