My chapter was, and still is, far below total, so we were always recruiting.
We participated in fall formal recruitment, and held a COB rush week early in the spring semester. Normally we got our "big" class in the fall and picked up 1 or 2 in the spring.
If someone expressed an interest in joining, though, we wouldn't make her wait until the next official rush - we would each make the effort to meet her, then the chapter would vote on whether to extend her a bid. We got several great women that way
If we had a NM class going at the time, and it was early enough in their NM period, she would catch up in her NM education and join them; otherwise, she met privately with the new member educator and was initiated by herself (and got her own separate NM class designation).
Now that my school has gone to deferred rush, my chapter holds a COB rush in the fall for sophomores and up, and will participate in formal rush at the beginning of spring semester.