Maybe because she thinks that since Shinobu cheated first, her actions are now justified. And even if she had the feeling that she cheated, the blonde bitch and the fuckboi would probably console her saying that what she did was not wrong. For all we know they could've been constantly manipulating her thoughts about Shinobu during the timeskip and painting him out to be a villian so she doesnt feel guilty as of now (not untill she learns the truth which may or may not matter if she is already in love with the fuckboi who blows her brains out every night in 100 different positions)