I am sorry. she is not entitled to full UC. If her father is paying her a regular allowance that is part of her income and must be declared. It is her business and the Benefit Agencies.
Likewise, if her son is living in her flat, even if only for a month or two, and the OP suggests something more permanent she hadn’t disclosed to the DWP that her 26 yr old working son,he’s got a good job in the City was living with her. then she must declare it as he will be attributed as sharing the expense of living in the flat, whether he pays her money for living there, or she lives there free.
Benefit fraud is theft and there is no way round that. This woman is stealing our money from our pockets, which most of us wish to see going to those in need.
Anyway, come the end of the financial year when the financial authorities make their annual reports to the HMRC, she will be caught up with and will have to repay it all back. Including money due over previous years for the council tax rebate she claimed but was not entitled to.
If she wants to risk getting a criminal record, then that is her problem, but once you cross the HMRC, especially if you end up in court, they will have you in their sights for decades after. It just isn't worth the risk.
However, I do agree, personal appearance is irrelevant. Appearing in the Dock at court is not in a beauty pagent and no one cares how they look, and I doubt whether the person concerned will be that bothered about how she looks at that point.