
because he, without understanding the situation or having ever met the mc, tried to demand for her to forgive her cousin which pissed her off because how presumptuous are you to demand someone else's pardon from the victim (or victim adjacent). so imagine someone raped you, and their mother came up to you and demanded you to forgive her son/daughter. you'd be preeeeetty pissed off, right?

oh and she never forced him to do anything, she told him that if he wanted to ask for favors, he needed the right decorum. he wanted her help (despite pissing her off previously), so he kneeled. he didn't have to kneel and could have left at anytime if he wanted. in fact, she could have just told him to leave and not help him but she still gave him a way to show his sincerity (him not complaining about kneeling and taking the picture frame to the head).
Just read the chapter where the MC forces Glenn to kneel for hours and then throws a picture frame at him, causing him to bleed. Is there a reason as to why she hates him so much?