So was DI Denton guity of conspiracy to murder?

She took the first payment from DS Akers (on behalf of the 'Caddy' AKA DI Matthew Cottan), and conspired to be part of the convoy that was to end in the murder of Tommy Hunter, but she did have a change of heart during the operation to kill him so it's debatable whether she was guilty. But the acceptance of the first payment, even if the rest of the money was later planted in her house unbeknownst to her, would be seen as de facto evidence of conspiracy to murder in the eyes of the law, irrespective of her later intentions.

Legally I'd say she was guilty. But morally I think she was a fundamentally honest cop, albeit a rather nutty and obsessive one.

Yes. She took a bribe from Cottan and agreed to help kill Tommy because she believed he killed the missing 15 y.o. girl.

She took the money to help arrange Tommy’s murder, so as a matter of law - yeah. But morally, she might’ve been in the right