Child Maintenance Order in relation to Inheritance

I divorced my wife in 2005 after being continually physically and mentally abused by her, resulting in me leaving the marital home and my son. She immediately applied to the CSA and as a disabled ex- serviceman, I was assessed at only £5.00 per week due to receiving a War Pension. At the point of reaching court and sorting the financial matters I was happy to agree to pay a top up by way of a child maintenance order which added an average of £178 per month. Before I had the opportunity to pay, my ex- wifes mother had contacted my employer and created such a furore that I ended up having to resign. I then essentially did not work ( and therefore could not pay the CMO) until August 2009 as I then became the main carer for my daughter and my mother, who was long term sick. I could only take part time employment at a salary much lower than I had earned previously and complied fully with the CSA, who informed me that nothing changed. In June 2010, my mother passed, and my ex- wife immediately applied to the CSA for a variance and has been sending through her solictor very threatening letters trying to retrospectively claim back the CMO from my inheritance, although my solicitor has stated that if you were not working, the maintenance orders do not accumulate. As this is completely out of my remit (and apologies for the essay), I'd be grateful for any advice regarding either the CMO or my late mothers inheritance.

I think it would depend on the size of the inheritance. There is a section on the CSA website that says a variation can be applied for if the nrp owns money or property equivalent to £65k or more. However if you are not working, and your inheritance was larger than that, I suppose the CSA would need to factor in long-term living costs.
You say you became the main carer for your daughter. Is this still the case and is she the only child of the marriage?
I'm afraid I don't know anything about the CMO but if it was voluntary I don't see how it could be enforced if not done through the CSA.