How to split Structural Maintenance work, to claim on Insurance/ split the cost 50/50

Maintenance

Hello,

Please help!

I have the share of a freehold in a house, which has been split into two flats. I own the 1st floor flat, which
I let out, the freeholder owns the downstairs flat.

The lady who owns the downstairs flat asked me to go halves on her with the buildings insurance, which I agreed to do. But I did not check to see if my name was on the insurance policy, we now have structural issues with the property, and my name is not on the insurance policy, so I cannot even make enquiries about a claim.

1. As my name is not listed as a policy holder ( my fault for not double checking ) can I challenge this, as I was invited to pay half of the house insurance fees, was the freeholder legally obligated to list my name down as a policy holder ?
2. The freeholder who lives downstairs is also refusing to claim the structural work that needs doing on the insurance, can I also challenge ie insist she put claim it on the insurance.
3. I told her that if we don't claim it on the insurance, that I am willing to pay half of the costs, as she jointly owns the building. She is refusing to pay, saying that she will only pay her 'fair share', she claims that more work needs doing on the upper floor, the structural survey says otherwise.

I feel as if she is trying to take advantage.

What is he best way to proceed, should I just seek legal representation and leave it in the hands of lawyers