Sentence:  She'd always had a thing for alpha males. Not that she had any intention of being bossed around, even if one had her best interests at heart. Her fascination with alphas was that they were a challenge. <WSD>Betas</WSD> didn't hold much of an appeal. 
Meaning of the word marked with <WSD> tags:  (beta male), a man who is less competent or desirable than an alpha male.