I am a the father of a man aged 45 with LD who like your niece is vulnerable in the real world. He has managed to hold down employment, originally under the sheltered placement scheme where the employers expectations took in to account his disability and only paid that proportion of his salary. Since he transferred employment following retirement of the previous employer, he has had to move in to regular employment and the expectation is that he should perform as any other employee with reasonable adjustments supported through the Access to Work Scheme, which does not take in to account capability levels . This has now come in to performance management, which he does not really understand and cannot grasp the importance of. So he may now be in a situation of dismissal under capability grounds, I am not allowed to get involved, he can only be represented by a work colleague or union rep. I also have to get up early each morning to take him to work as there is no direct bus route to his work place as they have restructured and the new place is on the other side of the town. If he gets dismissed he will not be entitled to benefits as we have allowed him to save most of his wages to secure his future. So he would not qualify for Universal Credit, only his PIP.
I say all this as a word of caution - I am also involved with many charities and bodies involved with people with LD and have spoken to a number of people with LD who have tried out employment , which has not worked and now find themselves having to fight to get back the benefits they received previously. If she does want to work for the social aspect keep within the allowed hours without affecting benefits, consider volunteering as many of the people who I know do. Contact your local Learning Disability Partnership Board who may be able to help with activities and volunteering opportunities. We are very fortunate in the North West to have some excellent groups to get people involved.