Tumblr is basically the only place I can do this kind of tiny Fandom detail, so I'm gonna do it. So, idk what the Fandom's opinion on this is, but I think Beatrice actually did love Donut and didn't want to sell her but was being forced to by her god-awful piece of garbage mother. The mother who was so misandrist that she viewed even boy cats as sperm donors to be used and thrown away. That was so toxic she couldn't understand that Bea actually did love Carl. Who very obviously was constantly manipulating her daughter and pressuring her to use and discard animals. Who named all of the cats after food items because she didn't want to have to think of actual names for them (also there's a lot of symbolism there with them being items that she consumes instead of living things.). I think Carl's arguing with Bea made it infinitely harder for her to give up Donut, although to an extent that's a good thing. But I think Bea was caught between her manipulative, abusive, controlling mother and her kind boyfriend who was insisting they keep the cat they both loved. But Carl never admitted he loved or even liked or wanted Donut until he and Bea broke up so his argument didn't carry enough weight.
I'm not trying to say that Bea was a good person, because she wasn't. She cheated on Carl and probably would have given Donut away in the end, no matter how much it hurt. But look at her song:
"Good girl, good girl, you're a good girl, my princess.
You're like a root beer float. Oh yes, oh yes.
I'd take it all back and never let you win. I wouldn't do it all over again.
I love you. I love you. I'm sorry, my princess.
It's so...sad. And fucked up. Bea loves Donut, she says so and calls her a good girl as a term of endearment, and she's saying she'd never have made her a show cat if she'd known it meant her mother would force her to sell Donut. She's telling her cat she wishes they could both just be free. All of the shows are what Bea's MOTHER wanted, not what Bea wanted. Bea wanted to sing to her and dance with her and cuddle with her cat. Then when everything happens she thinks Donut is dead and it *breaks* her. She treats Ferdinand like he's Donut just because she knows him and he has a vague connection to Donut. She just cries about her cat. This is what it would have been like for her if she'd given Donut away, but worse, because the guilt of knowing that she was going to sell Donut but she thinks Donut has died...it is crushing her. Look at how she changes the lyrics to the song:
"Good boy, good boy, you’re a good boy, Ferdinand. You’re no Gravy Boat. Oh no, oh no. I’d take it all back and let you in. I’d do it all over again. I’m sorry. I’m sorry. I’m sorry, Ferdinand. I should have let you in.”
She's calling him by Donut's name for him (I don't remember how she knows it.), and then expressing regret that she didn't let him in when Donut was in heat. That she didn't just give Donut what she wanted out of love. She'd do it again. She'd not show and would let Donut have the little family she wanted. It's so goddamned sad...and that's why I think Beatrice actually did love Donut, and that Donut's angry speech after the show makes this little bit of the story a true tragedy.