Suffice it to say that no character who marries for status or for financial gain is portrayed as having a happy marriage in Jane Austen's novels. The imprudence of marrying for security is shown many times as responsible for unhappy marriages where a couple tolerate each other, but grow more and more aware of their lack of love for one another.
The social stigma of marrying above or below one's social circle is a constant theme causing turmoil in her character's lives. Think how characters who marry above their circle are portrayed (are you led to like or dislike them?).
In Emma, I think that we are led to like characters who marry for love regardless of social rank, but be wary of characters who marry to gain rank. It would not be wise, in my opinion to assert that Jane Austen promotes marriage outside rank (Mr. Knightley reminds Emma of Harriet's lack of rank and warns that she ought not become too puffed up in her marital hopes. Since his reasoning is portrayed as clearer than Emma's, his would seem to be the opinion the author intends to emphasize as the norm.).
If you see examples clearly in opposition to this, cite them and stun your professor. :)
Austen in "Emma", describes marriage not only as something done for love, but also as something done for convenience. These are the two kinds of marriages in all her novels. In "Emma", an example of a marriage done for convenience is miss Taylor's marriage to Mr. Weston. this not only give her a rise in class level, but also provides her with securtiy for future. Unlike her, Emma knows that she would not die "an old maid". thus she does not feel the need to get married for convenience. Her marriage to Mr. Knightly is one based on love alone. Also, when talking about Austen's own attitude to love and marriage, we need to make note of her own personal life. Note that Austen was writing about her own time period, and her life would have an influence over what she wrote. Austen in "Emma", and all her other novels, tells her readers that they have a choice when it comes to marriage. This, could be influenced by the fact that she herself never married. so, if you are to answer questions about marriage and love, and Austen's own opinion, an insight to her personal life would be of much use. :)
In the Austen's novels, the notion of marriage was described not only as an alliance between families, a bound in which the spouse's love feelings have no place, but a merry companionship based on love and esteem, without excluding though the wife's economic subordination to her husband. To emphasize all written above, we just need to dart a glance at those merry marriages from Austen's novels: Catherine and Henry,Emma and Mr. Knightley,Fanny and Edmund etc.