This was resolved through Airbnb - who sided with us and issued a partial refund.
Nina was a very angry host and this feedback really is just the cherry on the top.
It's true that we asked for an early check-in, but we checked out at 11am as per her request. It's not a strange request for someone to ask if they can leave their luggage at their accommodation until their flight; all of our previous hosts have been more than understanding about this.
As for the internet, we didn't require any special connection. The work we were doing should be easily handled by any standard internet connection (emails, etc) however we speed tested the wifi on multiple occasions - and it simply wasn't working at all. It hovered around 0.03mbs, with 0.00mbs upload speed.
She did offer to cancel our booking (not refunding the nights we stayed) and we did look for alternative accommodation. Unfortunately due to the last minute nature there were none available - all of this was communicated with Nina.
We did come to an arrangement whereby Nina would cover the costs of our internet usage elsewhere (mobile internet and cafes), however when we followed up on this at checkout, Nina ignored the arrangement and refused to reimburse us.
We ended up having to mediate through AirBnB, who sided with us and gave us a partial refund for the lack of internet.
Nina's angry feedback attests to our experience with her, and is also unfortunately a twist on the truth.
Ultimately, things happen (such as the Internet being down) but it was Nina's hostile disposition and threatening messages which really made this an unpleasant experience. All in all a very weird stay.