A few questions for OP:
1. Did a solicitor handle the administration of the estate?
2. If so, why did he\she not undertake to do this job? What did he\she say about it?
3. Like Vanilla, I find it strange that four different solicitors showed no interest. Is it possible that there is some perceived difficulty in dealing with your mother, such as agreeing an acceptable fee? (no criticism intended - many many older clients baulk at the cost of almost everything these days) If so, how much do you think your mother would willingly pay a solicitor to resolve the lack of paper title? How much would be too much for her?
If there is no plan to sell or re-mortgage the property in her lifetime, your mother might well be making the right decision if she decides to simply leave the problem sit for the next generation to sort out: No point in spending money that she might need to achieve something she doesn't particularly need.