In Twelfth Night, would Olivia rejecting Orsino's proposal be a good example of the reinforcement or challenging of the cultural issue of courtship?
I think you need to focus on the point that Shakespeare is making in this riotous comedy about love and how it impacts us as human beings. Love in described in this play variously as a kind of "madness" and as a "sickness" that comes upon us suddenly. Shakespeare seems to use the rejection of Olivia to poke fun at the way that we as supposedly sane, sensible and rational human beings can suddenly be turned upside down by the power of love. Consider what we are told about Olivia and her refusal of Orsino in Act I scene i:
The element itself, till seven years' heat,
Shall not behold her face at ample view;
But like a cloistress she will veiled walk,
And water once a day her chamber round
With eye-offending brine - all this to season
A brother's dead love, which she would keep fresh
And lasting in her sad remembrance.
This is an extreme promise, but look how quickly Olivia abandons it when Cesario (Viola) comes along, who is only a henchman of Orsino! Love forces her to abandon the possibility of a very attractive marriage to one who is her social equal and makes her chase and pursue (in the way that she has made Orsino pursue her) Cesario to comic effect. The lesson is clear - love does not consider rationalism and logic when it strikes, and we are often struck suddenly and to disastrous effect!