As someone with a degree in Wildlife Science, though I'm not in the field any more, who studies wolves pretty deeply as part of course work for said degree I can tell you that's simply not true.

There are absolutely alpha females.

Further, pack hierarchies have been observed to be somewhat fluid. The original research that designated alphas, betas, deltas, gammas, and omegas hasn't really held up to scrutiny. Shenkel, who first coined the term applied it to both males and females and recognized that leadership fell to both. It's a partnership. Alphas are the only breeding pair of the pack. Males don't bestie alpha status to a female by choosing her as a mate. She earns her own status.

Mech, who used the term in his 1970 book was more selective in his use of the term (excluding females basically) and applied the behavior to captive wolves rather than wild pack. In other words, packs under stress where behavior is abnormal to natural wolf acts in the wild.