Why would a woman not be happy about a sudden, surprise proposal?

My younger 22 year-old cousin got proposed on March. Her now fiance is 5 years older than her. She said yes. However, she then admitted to saying yes out of pressure because he proposed in front of our family and friends. She had no idea we were all invited. It was really a surprise party. Yet, she didn't seem excited at all. She looked very nervous, not out happiness. Her expression was a ''What the hell is going on'' type... not a happy face.

Their date wedding was orginally set for Sept. She postponed it without a date set on, claiming she isn't ready for marriage yet. What? Not ready? Even if the woman were to be clueless that he's going to propose... wouldn't that generally be every woman's happiness, what most want? Why wouldn't a woman be happy about a sudden, surprise proposal?
Why would a woman not be happy about a sudden, surprise proposal?
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