In this case, Mary's reaction that ends up devastating Edmund, could be explainable. She could be desperately trying to save her brother.

No while Henry's reputation WOULD suffer in soeme circles, it would nto do him any real damage. Mary's reaction was chiefly to do with fear that the scandal would harm her own relationship with Edmund. He's not now going ot marry the sister of the man who has just seduced and run off iwth his own sister. Mary hopes that if She could calm things down, and if Henry could marry Maria, it would change things and hte Bertrams would be willing to overlook the whole scandal and agree to her marrying Edmund. She mgiht even get some kudoes from them for sorting out a sensible "worldly" solution to the problem, for persuading H to marry Maria and by "good dinners" family support and generous expenditure, getting Maria received again in some circles.. Again she's misjudged her company as Edmudn and SIr T are not likely to consider this an acceptable solution.