It's very normal for a mare to show to geldings. They can't quite tell the difference between stallions and geldings. I have a mare that loved to shove her butt under him to a point he had to mount because she got under him. Otherwise he will get very mad and bite or strike at her to get rid of her.
Proud Partner Owner of Me Too Radical, Top 10 PQHA Quality Improvement Program Futurity. Sire of AQHA, NSBA, and NRHA champions. Sweet, gentle, excellent mover, excellent temperment, and so much more. Standing in Indiana.