I hear she is the worst part of the show.
Who? I think that you don't talk about Kate Mulgrew?! She is considered by critics & viewers as one of the best parts of OITNB's ensemble, with Uzo Aduba, Danielle Brooks, etc... . Of course, we can dislike her facial/gestural and corporal expressions are her. That and her humor. In short, a true character part!
However, it seems that Taylor Schilling's character, Piper, who was supposed to be the new kid of the block, pretty, smart and crazy in love was considered as the weakest link. (I remember that Mulgrew, right the s2 or 3, tried to explain why people didn't manage to like and/or be involved with Piper's character). As for her passionate lovestory with Pepron's character, Alex Vause, I don't know for you but for me, it was forced and worst, unconvincing.
Result: producers decided to let Piper leave the prison, under the reason of an early release and to let the actress coming back as guest-star for the 7th and last season. I don't know if Schilling's acting was weak or her character was
uninteresting but the whole was difficult to watch...

-> I felt more interested by Suzanne /Tasha / Poussey / Cindy and Caputo storylines.