Is anyone here a surveyor?

As far as I understand it:

The landlord owns the flat, the freehold is with Vision Homes, who use Action Homes to manage the freehold.

Therefore Action Homes are responsible for all outside, communal, and access repairs/issues etc, on behalf of Vision Homes.

ok, so, your friend/landlord needs to formally communicate with the managing agent stating that the freeholder has failed to meet it's obligations under her lease, and that if they cannot (in a reasonable period of time) provide a plan to rectify the situation she will be instructing her solicitors to recover losses incurred as a result of this failure.

you have a contract with her only, and she has a liability to you.
she has a contract with the freeholder, and the freeholder has a liability to her.
the freeholder has a contract with the managing agent, and the managing agent has a liability to the freeholder.
No-one has a cotract with Nisa.
The freeholder has buildings insurance to deal with this.

If your landlord writes to the agent (who is a representative of the freeholder) and gets no joy, then the managing agent is liable to the freeholder for failing to ensure that the freeholders contractual commitments are met.