It is quite possible that she would not be better off working.
i have been on benefit twice after redundancy and i can tell you it was a bloody miserable existence.
problems i faced going back to work. well firstly the job itself. i needed hours between 9.30am and 3.30pm. this was my absolute limit with regard to childcare at the time, and this was with help. i dont drive and couldn't afford to learn. even the job i have now takes an hour to travel back from whether i walk or take two buses. there was nothing available any closer to my home. so say i didnt have help...two buses in a morning to get ds to his school (not very close to us but he was bullied at our local one). then another one back to take dd to nursery, then two more to work, arriving at approx. 10.30am.
then at 2.30pm, two more buses to pick ds up from school and another back to pick dd up from nursery, then a 20 minute walk back.
i dont suppose there are many jobs out there with hours like that and if there were, to make that kind of job worthwhile it would have to be every day and to do that it would cost 5 days worth of full day nursery sessions. (yes tc will pay 80% of that if they pay up) childminders are few and far between here and i did look into it but there were none who could pick up ds from school.
the tax credit situation is a whole different story. when i first applied i did not get any payments for three months. nursery do not accept none payment of tc as a reasonable excuse for being late with fees..miss a week and you're out, simple as that. im lucky i have credit cards as i used them to live on for a while, but not everyone can get a credit card, or a loan. not everyone has friends or family to help with childcare. tc are notoriously unreliable as are my local council who ballsed up my claim for part housing benefit every time they touched it.
its perhaps not that some people cant work because they will be worse off, but because they cant afford to be any worse off than they are already. getting off benefit is not as easy as simply changing your job. its not as easy as saying "the jobs are out there if you look hard enough". im not saying its the same for all but some peoples situations/circumstances make it virtually impossible. it takes a great deal of skilfull juggling to get it right.
and all that takes a long time to explain to someone who is clearly looking down their nose at you because you claim benefit, so it does become much easier to say "because i'll be worse off".