Praise be to Allaah.
Cutting hair to make it all of equal length, reaching the shoulders or ears is OK, so long as that does not involve resembling the kuffaar. Resembling the kuffaar is haraam even if it is in regard to something that in principle is permitted.
With regard to cutting some of the hair and leaving some of it, that is not permitted. This is the hairstyle which was forbidden by the Prophet (peace and blessings of Allaah be upon him), as is narrated in Saheeh al-Bukhaari and elsewhere.
This ruling applies to both men and women. It is OK to cut the hair and make it of equal length so long as that does not involve resembling the kuffaar, or making men resemble women and vice versa. Women should not cut their hair short in a manner that resembles men’s hairstyles.