The Mishnah before us deals with a young woman whose fine is not paid to her father but to herself. The Gemara clarifies that this is not one case but two separate cases.
The two cases in the Mishnah:
"Yesomah" - an orphan girl who has no father. Since she is an orphan, every fine and every penalty payment that the offender owes is paid to her and not to her father.
"Nis'arsah v'nisgarshah" - she became betrothed and was then divorced. This applies even when she does have a father. The ruling follows the opinion of Rabbi Akiva that we learned in Mishnah 3: once she has been betrothed even a single time - even though she is not married now - the fine no longer goes to the father but to her.
In both of these cases, then, the fine is paid to her herself.
The words of Rabbi Elazar:
Rabbi Elazar points out that in a case of seduction, the seducer is exempt from paying the fine, since she consented of her own will. The obligation to pay exists only where the father is the one who receives the fine; but when she herself is the one meant to receive the fine, and she is the one who agreed to be seduced, he need not pay - after all, there were two consenting parties here.
By contrast, when he forced himself upon her, the fine certainly stands. In such a case it is paid to her and not to her father: either because she has no father at all, or because the father has no claim to it from the moment she became betrothed and was divorced from that betrothal.
In summary: in this Mishnah we learned two cases in which the fine is paid to the young woman herself and not to her father - an orphan who has no father, and a girl who became betrothed and was divorced, following the opinion of Rabbi Akiva. To this Rabbi Elazar adds the distinction between a seducer and a rapist: the seducer is exempt from the fine, since the one who is meant to receive it consented of her own will, while the rapist is liable, and the fine is paid to her.