Jane had been exercising self control over herself ever since Frank Churchill had persuaded her to enter into the secret engagement. She had also been feeling guilty because her conscience told her she was acting contrary to her principles.

Marianne Dashwood never attemtpted to make any effort for self control, when Willoughby left her, she wanted to show her emotions to everyone, she wanted everyone to know how unhappy she was.

Jane had been doing her best not to break down, not to let anyone know of her misery, but in the end it was too much for her, and her health broke down.

Even Elinor might have broken down if her circumstances were the same as Jane's. Unlike Jane, Elinor had no feelings of guilt as there was no secret engagement between her and Edward (though Marianne thought there might have been!), it was Lucy to whom Edward was secretly engaged, this made Elinor unhappy, but she had nothing to reproach herself with. If Elinor had been in Jane's situation instead -- if Edward had not been engaged to Lucy and had persuaded Elinor to a secret engagement, and then flirted with the rich Miss Morton to conceal it, it could be possible that Elinor would suffer the same feelings as Jane did.

Moreover, in addition to her misery over Frank and Emma, Jane was also preparing to leave her family and take on the job of a governess -- and wonder what kind of employer a dear friend of Mrs Elton's sister might be.

As Mr Knightley said of Jane in chap 51 --
"We must look to her one fault, and remember that she had done a wrong thing in consenting to the engagement, to bear that she should have been in such a state of punishment."