I'm so sorry.

Maybe you can put your guilty feelings in perspective by imagining that you had died & your sister had lived:

She would have the same feelings.

but you know that she loved you & that the argument would have been mended in time, & you wouldn't want your sister to feel guilty.

You would want her to remember you with the love that you both know was there all the time.

Maybe write her a letter telling her all these things and how much you love her, miss her, and all your good memories together. Keep a copy and put one on her head stone.

You've received good advice, you do need to think past the disagreement you were having and realize that you would have most certainly made up. The idea of writing a letter is a good one. My daughter was 13 when she died 2 1/2 years ago and she is survived by a sister 4 years older as well. My other daughter also went through some guilt of feeling like she wasn't the best big sister she could be, but has realized really how much they loved each other and that minor recent disagreements really didn't matter anymore.
You won't lose memories of her......but her death is so recent you need to be kind to yourself. Lean into your grief and let yourself cry when you need to, don't rush it and don't minimize your feelings or allow anyone else to either.
The holidays coming up will be hard and if you decide to do something, plan ahead but try not to be too elaborate about it and be willing to back out of your plans if you get to those days and you can't handle it. Also, you might want to try something to honor your sister during the holiday season, donate to or volunteer for her favorite cause. Something I've heard of but haven't tried is writing letters to our loved ones, reading them on Christmas Day but leaving them in something like a stocking till the following year. Then you can get them out and read them a year later and see how much you've grown during the year.
Angela