Hi and thanks in advance to any help received

My Partner is having trouble at work and would like opinions as what action to take

Being Employed for nearly 3 years she has had some issues with health and i am concerned some of these are work related and caused buy harassment.
She has taken sick leave to the extent of not having any sick leave left and some unpayed days . All these health issues have been authenticated with Doctors certificates .
She is in a service technician role as stated for 3 years and has recently been asked to attend a meeting concerning her absence and performance . They changed her familiar run with another unfamiliar to her . This is causing her slight stress and due to her not knowing the area , parking arrangements and customer needs this is slowing her down and she isnt performing at her usual capacity . She has mentioned this on several occasions to her supervisor and has been told if you don't like it leave. This response is concerning to me and makes her feel not wanted in ways understandably . This is not a response i would expect or like to hear myself. She was asked to attend a meeting with a higher manager plus the supervisor and in that meeting was told that enough was enough and she was letting down the team . Also more alarming was that she was told that other employees had resigned because of her absence due to her health issues. Not knowing the law i find this disgraceful and undue accusations . She has notice in the work environment that nobody will talk to her anymore and feels alienated . Why so i ask . It seems obvious to me .Now moving on to the performance based accusations. Prior to the new unfamiliar run given to her she achieved all but a few monthly bonuses that are granted due to KPIs being completed . This to me would suggest her performance prior to this was satisfactory . The manager also suggested she could resign if she liked ...more pressure applied and unsatisfactory to me. She isn't familiar with workplace laws and feels she has to deal with whatever they seem to dish up.I disagree . They have told her to make a decision by   Friday with another meeting and this creates in my eyes more pressure that i am afraid will have more effects on her health .
Is this normal practice?
Should she be subjected to this form of unprofessional behavior, criticism and accusations ?
I have also looked at her work load and calculating the daily KPIs recently given suggests and unachievable and unrealistic achievable target.

How can i help her and do i have genuine concern on the way she is being treated

Any help would be greatly appreciated

Thanks in advance
Larry
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Have a look into constructive dismissal, which is illegal.

This is the correct category for this scenario.