Hi Louisa, thanks for commenting. In fact, it’s a bit more complicated than that. The problem is about collective nouns (i.e. singular nouns that denote a group of people). In British English (wich is my favourite variety), you often use plural pronouns on collective nouns (‘the police are chasing a criminal’), in American English singular pronouns are more widespread (‘the police is chasing a criminal’). It also depends on whether your focus is on the group as a whole or its members individually. See also here. But to say ‘the brand’s target group is single women’, for instance, would be perfectly correct. In fact, you can use it either way.

I think it needs to be:
..group is …