How to handle a difficult coworker?

I have a somewhat new coworker who started at the start of this year. She gives me more work than what I can manage regarding her behaviour. I work in the disability industry and she continues to annoy/upset clients regularly. She talks about clients troubles, nags them or repetitively asks them questions which annoys them or confuses them. I have often difused the situation multiple times.

She does not learn very fast, I have had to teach her 5 times how to use the air conditioner in the car but still asks me to do it while I am driving because she doesn't know how to.

She was also responsible for looking after someones expenses and calculate how much they spent. She expected me to know but I was busy with someone else, she kept nagging me to figure it out but I told her each time I was looking after someone elses expenses and not responsible for theirs. She asked me to report it to the clients relatives which I again responded the same answer. She got very angry and I was very pissed off with her.

Most of my coworkers cannot handle her at all and I am usually left with her because I have patience. I took 2 weeks off this month so I can destress. Last time I was working with her I was shaking from stress.

These are some scenarios. She has also broken some workplace rules regarding the relationship between clients and workers. I reported on behalf of the client.

Other than this she is literally a nightmare! How do you handle someone like her? I've spoken to my manager and says she still needs time to adjust and needs reassurance in her role which I provide. But she lacks basic common sense
How to handle a difficult coworker?
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