I dont know how to deal with my sister?

My sister sometimes is very demanding. She is those person who need answer right away to her text messages otherwise she gets mad if I dont answer right away or I take until the next day to answer. Im with a bit of a cold and we saw each other in person on Sunday so she saw me how was I. Then yesterday in the morning she texted me to ask me how was I and I did reply her that I think I was getting better, then again today in the morning she texted me again to ask me how was I and I did not answer. Well today at night she call my mom to ask how she was as she call my mom everyday and told my mom that why I did not replied to her todays messages, She got mad because I did not answer to her texts. She is hooked to her cell phone at all time. Im not like her and I asnwer when I want not when she demands me to answer. Of course I won't answer her one week later, but i mean it was just one day I did not answer and she got pretty pissed off. I mean she saw me on Sunday then yesterday she texted me and I answer and today she asked me again but this time i did not reply and she got really mad. My sister does not live with me of course.

I dont know how to deal with my sister?
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