Lady Russell's main argument against Wentworth was that he had nothing concrete to offer. HE was certain his future was bright, but who really knew? In a society where a woman cannot escape a bad marriage, young Frederick Wentworth was a huge gamble. He wasn't even from a family they knew, so even his character was uncertain. If you're marrying someone from the same neighborhood you at least know how he acts when rain spoils his parade.

Now he's back and, oops, fortune made, respected by his comrades--looks like that gamble would have paid off! I'm sure Lady Russell is glad to find something wrong with the man! Perhaps she's thinking that if he is really was worthy of Anne he will now be mature enough to understand Lady Russell's earlier reservations.