How do I prove I am carer?

Hi everyone,
Hope you are all staying strong and well during this awful time. I am sorry to bother you, but I am at my wits end with my sister over mums care.
I am a professional home care worker and for the last 6 years have visited my elderly parents on my day off, every Thursday to help with anything and everything they may need. (Bill’s, cleaning, cooking, personal care etc…).
Unfortunately, my sister has decided during this lockdown (didnt say anything on the previous one!) I am not allowed to visit and am breaking the law and putting mum and dad at risk.
Dad can cope with the shopping but not much else and mum has developed mild cognitive impairment, so my help is essential as they wouldn’t have house or car insurance if I hadn’t noticed it needed doing.
I have tried to explain about government guidelines permitting me to carry on providing care, I have sent her all relevant information I can find and I have also given the same information to mum and dad, including what ppe I should be wearing. My job means I am completely compliant with p.h.e requirements, but she will not let up.
My sister rings my parent every day, relentlessly bullying mum and dad over my visiting and I feel I need a permission letter from Boris Johnson himself!
This is causing huge mental stress on my lovely, gentle mum and my poor dad who seems to be scared of my sister. I am struggling with sleeping and eating due to this worry.
What else can I do???
Any advice would be appreciated.
Jo. X

Your sister’s behaviour is very strange indeed.
She has NO right to tell your mum and dad who they can and cannot see.
Next time she rings you, record her call.
How old is she?

Thanks for posting. My sister is 56, 10yrs older than me. She never really takes an interest in mums health as it doesn’t register that mum is getting older and needs support; my sister still thinks mum is as she was when she was 50!
I know everything about mums needs, medical and mental, i go to all appointments with her and all medical staff have been welcoming and accommodating. I also research everything I can in order to provide the best help I can, but because she wont believe me when I say I can continue visiting through the pandemic, it’s made me feel unsure and useless, even though my job is as a professional home care worker, so I know all the rules and procedures and I follow them to the letter with my ppe and social distancing.
The doubt that she has cast on my ability to care and help mum has really hurt and mum is in tears.
The only other thing I can think of is to get a letter from her gp, acknowledging I am her carer and am allowed to visit. Mum really likes an respects her doctor, so am hoping it will put an end to it. I will ask the surgery on Thursday.
Jo. X