She wants Sunak out which is different. She doesn't have to form her own party - she could just not align to any. Allowing her into the Labour party shows weakness by Starmer imo - he shouldn't need her, or anyone like her, to convince swing voters to vote Labour. Core Tory voters are not going...
By defecting to Labour, who have accepted her, it gives the impression that they are accepting her views too. Surely the honest and honourable thing would have to become independent?