It's not really your problem directly, it's the state's or your mum's. The only issue is whether you want to continue to subsidise her. Depending on when she was born, she might be reaching her state pension age in 5 years anyway.
You know her best - what do you think her mental state is like? She may be very comfortable in her current situation rather than lazy or she may be very frightened of what a big change it would be to work when she has no experience.
In the past, benefits were easier to access and remain on. Now they are harder to enter and easier to exit. You have to remember that there have been big changes over the last few decades.
It's actually quite difficult to remain on job seekers benefit for a lengthy period of time - are you sure this is what she is on or do you think she might be on a sickness or disability benefit? With present day job seeking, the DWP work coach will put people on full time job searching who are not getting any jobs and sanction them for not doing this or not attending interviews, for example. Are you worried that her behaviour will mean that she will be sanctioned by the DWP?
Back in the 80s/90s, perhaps up to the 00s, unemployment figures were alleged to be massaged by people being switched onto Incapacity Benefit. At its peak, 1 in 5 working age people in my city were on IB. Many people were ported onto it from child related and job seeker related benefits. Again, that's hardly the fault of the claimant that it was made so easy to claim sickness benefits in the past - now it is very hard.
I don't know when it changed but if your mum is a single mum, until x year, single parents could legitimately remain on income support and child related benefits until their youngest child were in their (mid?) teens. Now it's been drastically reduced. That might account for a lengthy period of her working life. So that's completely legit.