Aubert's and Sellers' stats are comparable. The Big Sky all-conf. article didn't cite defensive stats, so I took a look on the Big Sky Site.
Fielding Percentage: Aubert --.974; Sellers--.980. Ratio of chances to put out: Aubert--228 chances to 224 putouts; Sellers--351 chances to 333 put outs (yes, she plays @ 1b). Assists: Aubert--18; Sellers--11 (very high for a 1b). Double Plays: Aubert--6; Sellers--11. ALSO... There's a baseball stat that's not included in the Big Sky Conf. softball stats: unassisted double plays. I'm going by memory, but think Sellers had 5-6 unassisted plays, where (with a runner on 1st) she snagged a hot grounder, tagged first and then tagged the runner diving back to first. She had a gem in the second game vs. SUU where she dove on a squibbler, scrambled up & tagged 1st, then threw to 2b to get the runner (on a tag by ss). I cite these, because they are plays that involve first basemen more than other players.
Statistically, then, Sellers has clearly superior stats on offense and defense. What's not considered are factors like leadership, style, attitude etc. My thoughts are that most coaches will opt for the senior in situations that are very comparable.
There have been, however, some odd votes over the past two years. In 2017 Delene Colburn was snubbed for both first team and MVP when she was the clear league MVP (she finished 2nd in mvp voting). What no one will ever know is the existence of bias. It has happened a lot in men's BB, and in football, where some unknown (Big Sky) coach will never vote for players from a certain team. I've wondered that regarding softball... but that boils down to sour grapes on my part. I actually think that awards this season (POW) and SIX Big Sky All-conference awards, put Montana into good company. I personally believe that Jessica McAlister is the best catcher in the Big Sky (she has by far the best "caught stealing" stats), but Rachel Menlove of PSU and Emma Brockman (UNC) are both very good, so hon. mention for Jessica puts her into good company. I also think it's awesome that the Big Sky honored Montana's two seniors, Maddy Stenby (1st team All-Conf utility pitcher) and Colleen Driscoll (hon.mention starting pitcher).
I guess that all conference awards are meant to be argued & contested. But when statistics so clearly indicate Sellers as the league's all-around best player, it's something that's worthy of challenge.