So sorry to hear this OP. It's lovely you were there with her at the end. This was true for me with my dad too, and I find it a great comfort looking back.
I lost my dad a month ago. I actually found the immediate aftermath was tolerable because there was so much to organise with the funeral, informing people etc. It's actually somewhat harder now, as the grief is now really hitting me. Also, don't underestimate the toll on you the last few weeks will have taken, supporting her through her end of life path. My dad died at home with myself, mom and my brother as his carers and it was exhausting in the extreme, literally by far the hardest thing I have ever done......
So if you work, I would be careful about rushing back too soon. I only returned to work last week, and that was on reduced hours (I got a fit note from the GP to specify this).
Your experience may be very different, but I just wanted to say, just because you may appear to be coping initially, you still need to look after yourself.
(God I know that sounds negative and pessimistic, sorry, but I just wanted to share my experience. My cousin told me at dad's funeral that she was signed off for 6 weeks after losing her bother, and hearing that helped in a strange way, as itade me realise I wasn't unusual in taking time to recover).