I'm at a loss to find anything that confirms that Mafalda was a "very bad person". She was certainly working for the Ministry both before and after Pius Thicknesse took over, but there's no special indication that she was in any sort of position of authority or that she wasn't simply keeping her head down and getting on with her job.
Percy (in Deathly Hallows) mentions that by the point that it had become obvious that the Ministry was under the control of dark forces, that anyone who quits the Ministry would probably be labelled a traitor, with all the consequences that implies to them and their families.
‘It’s been coming on for a while,’ said Percy, mopping his eyes under
his glasses with a corner of his travelling cloak. ‘But I had to find
a way out and it’s not so easy at the Ministry, they’re imprisoning
traitors all the time. I managed to make contact with Aberforth and he
tipped me off ten minutes ago that Hogwarts was going to make a fight
of it, so here I am.’
Best guess is that Hopkirk was actually quite a pleasant person, whose job simply involved sending letters and missives on behalf of more powerful people.
As noted in a comment, she does take the time to go above and beyond when it comes to signing off her letters, implying that she's normally quite cheerful.
We would also ask you to remember that any magical activity which risks notice by members of the non-magical community (Muggles) is a serious offence, under section 13 of the International Confederation of Warlocks’ Statute of Secrecy.
Enjoy your holidays!
Harry Potter and the Chamber of Secrets: Chapter 2 - Dobby's Warning
As you have already received an official warning for a previous offence under Section 13 of the International Confederation of Warlocks’ Statute of Secrecy, we regret to inform you that your presence is required at a disciplinary hearing at the Ministry of Magic at 9 a.m. on the twelfth of August.
Hoping you are well,
Harry Potter and the Order of the Phoenix: Chapter 2 — A Peck of Owls