Trisha already knew…
She had realized it a long time ago. It didn't matter how hard she swung her blade, or improved her form, or desired victory… she was never going to get it.
Not against someone like Rey.
As the boy closed in on her after parrying her final move, she felt herself descend into a haze.
'I thought… if I hit him one time, I could prove something to myself… and to him. If I managed to do it, then he wouldn't have been such a liar.'
All this time, Rey portrayed himself as weak but skilled. It lit a flame within her that even she could become stronger if she kept at her training and adhered to his advice.
She indeed became stronger, but the backlash of betrayal that came from her new perception of Rey wasn't something she could ignore. She tried to, but was unsuccessful at every turn.
It seemed like Rey lied to her all along.