Critical illness insurance

First time post so hopefully this is in the right place for advice.

My 25 year old partner’s Mum was diagnosed with MS about 10 years ago when she was around 40 years old.

We’re currently trying to arrange life assurance and critical illness cover but the broker has advised us my partner can’t get covered for MS until she’s at least the age her Mum was when diagnosed.

Does anyone have any advice or any specific insurers/brokers we can go to, to make sure she’s covered now?

thanks in advance,