Jane's use of tact and consideration to avoid offending Bertha while discussing the fit of her dress is an example of positive interpersonal skills, contrasting with the interactions between Marjorie and Bernice which lack such tact.
The sentence in question suggests that Jane had the opportunity to offend Bertha by commenting negatively on the fit of her dress; however, she opted to approach the situation with tact and consideration. Tact is a sensitivity to the situation at hand and the ability to avoid giving offense or to make the person feel at ease, while consideration involves thoughtfulness towards others' feelings.
The use of these traits to mitigate a potentially hurtful truth is highlighted as a positive interpersonal skill. Jane's approach contrasts with the harsh interactions between Marjorie and Bernice, where Marjorie lacks the tact Jane displayed, leading to Bernice's feelings getting hurt.