Update: Answered in the comments much more thoroughly and succinctly than I can summarize, so head below for some great answers.
She’s apparently the warrant officer, which I’ve seen hypothetical explanations state is the XO, the second in command, but she explicitly states that she is the third officer at the end of the movie, and throughout The movie she is the pilot and she checks the electrician’s work and volunteers to go fight the alien first, and also states that she is in command while the others were off the ship.
So was Kane second in command?
And what is a warrant officer?
Thank you
BTW if there is a crazy Aliens expert, I have a few tiny questions that only a crazy fan who literally read everything ever written and watched every interview about the movie might be able to answer.
Adding on to this, TECHNICALLY speaking the freshest butter bar (lowest ranking commissioned) outranks the highest warrant. However, just as it would be foolish for a lieutenant to try and pull rank on their grizzled platoon sergeant, it would be foolish for an officer to dismiss the advice of a warrant for all of the reasons stated above.
Also, I find the biggest distinction between warrants and other officers is their attitude on command, which I think fits very well with discussing Ripley’s role on the ship. The warrants I have worked with typically have little to no interest in being in charge of other people, outside of a small team of folks dedicated to a common mission (e.g. a vehicle maintenance shop, supply warehouse crew, etc). If they wanted to be supervisors, they either would have remained NCOs or commissioned as lieutenants rather than warrants. So, Ripley being put in a position where she is responsible for others is probably both not in her wheelhouse, and actually antithetical to her desires. That’s always gone a long way for me as for as explaining her prickliness early on (especially relating to Yafet Kotto and Harry Dean Stanton’s blue collar “enlisted man” characters).