No they will have other evidence, even if Barbs not cooperating they can still get him for something, even if it's just the breach of the EPO, but they likely have other evidance of what Chris has done.
Honestly I think she would, but it might take some time and it might be as rambling as Chris's letters are - I think Barbs a Sun Downer it was coverd in other threads but the long an short of it is She's more functional in the morning but as the day goes on she get's incrementally worse in her faculties and as she ages there is less good time available. If that Crash linked above was Her mid day would seem about right for someone in that condition (and general age) to get confused and getting into a crash.
Part of me does wonder though if it might have been intentional, I really doubt it but Barb might have the odd moment where she does just want her life to end she has not had contact with someone normal for years (that we know of) and she's left alone in her mess of a house with a son with the brain of a bonkers 6 year old.
I really do doubt it, if Barb is as mentally compromised as we suspect it wouldn't be hard for Chris to put 2 and 2 together and come up with 5.
Some elderly people with dementia and other conditions can display weirdly sexual behaviour and combine that with Chris being intellectually sub normal and having a fixation on Sex and a disgusting willingness talked openly in the past about thoughts of fucking his mother and defending incest in the past it was only a matter of time before this happened.
It ran out after a 5 day period, it's normally used in cases of Elder abuse like not feeding or careing for someone bedbound while the pearson supposedly caring for them sits on there arse playing games, drinking or smoking weed if I am recalling it correctly it's so that the Authorities can check on the physical, mental and legal condition of the Elderly person in question to make sure they are not getting taken advantage of Chris just happened to have fucked him mum and stole $750 from her as well causing him to be arrested.