Earlier this year, it emerged that Lori Loughlin and Ryan Eggold will leave the series at the end of the season.
Grimes has now admitted that she is unhappy with their final episodes.
"The writers don't really do the characters that are leaving the show much justice," she told TV Line. "Much like Rob [Estes], who didn't get much of an exit, I think it's going to be kind of a similar storyline."
Grimes described Loughlin as "amazing" but appeared to criticise 90210's showrunner Rebecca Sinclair, who is also leaving the series at the end of the season.
She said: "I'm thrilled for a change."
90210 airs on Mondays at 8/7c on The CW in the US and on Tuesdays at 9pm on E4 in the UK.