Responsa for Yevamot 213:13

והרי ביאה דבעל כרחה

— Both are pleased [to be married to each other]<span class="x" onmousemove="('comment',' Despite the objections pointed out by Beth Shammai. ');">³⁸</span> in order that they may be known as married people.<span class="x" onmousemove="('comment',' The possible loss does not, therefore, prevent a man from marrying a minor. ');">³⁹</span> BETH SHAMMAI RULED&nbsp;… AGAINST A HUSBAND etc. R. Oshaia stated: She may<span class="x" onmousemove="('comment',' According to Beth Hillel who allow the right of refusal even against a levir. ');">⁴⁰</span> make a declaration of refusal in respect of his ma'amar<span class="x" onmousemove="('comment',' If the levir made a ma'amar, she can annul it by mi'un, and no divorce is required. ');">⁴¹</span> but she has no right to make a declaration of refusal in respect of his levirate bond.<span class="x" onmousemove="('comment',' Only halizah can sever the levirate bond. In ordinary cases where the levir addressed to the yebamah a ma'amar, she requires for her freedom both a divorce to annul the effect of the ma'amar, and halizah to sever the levirate bond. ');">⁴²</span> Said R. Hisda: What is R. Oshaia's reason? — She has the power to annul a ma'amar which is effected with her consent; she has no power, however, to sever the levirate bond since it is binding on her against her will.<span class="x" onmousemove="('comment',' Because it is due to her marriage with the deceased brother, which, since she did not exercise her right of refusal against him, remained valid. ');">⁴³</span> But, surely, [levirate marriage by] cohabitation may be effected against her will<span class="x" onmousemove="('comment',' Cf. supra 53b, 54a. ');">⁴⁴</span>

Teshuvot Maharam