Hi discofever,
I am an ASW - it is part of my job to section people .
People are usually sectioned when they are a risk to themselves or others, and it's always a last resort.
SIL will possibly have a period of assessment before starting on meds. Alternatively, if her doctor already has a good idea of what the issues are, she might start on meds sooner. Hospitals avoid forcibly medicating people unless really, really, really necessary.
SIL may or may be allowed some leave from the ward, probably for brief periods with another person, once they feel she is not an immediate risk.
She will probably be on a section 2. This lasts for UP TO 28 days, but she can be discharged sooner if well. Alternativly if she unwell she can assessed for another section.
Most importantly, she has rights to appeal for her release, as does her nearest relative (husband if she has one). The ward can tell you more.
I can try and answer specific questions if you have any.
all the best for SIL's recovery.