I can't imagine how hard this is for you skp2bear. In some ways I think that being able to prepare oneself for a loved one passing is helpful, but in another way having it all impending must make life very hard to bear sometimes.

I'm sure that your mum knows that you're there for her and that you love her and that you are making the ultimate gift that you can give to her, to ease her passing to the best of your ability.

Please be gentle with yourself. There is nothing wrong with tears; they are an expression of intense emotion that you surely must be feeling right now. If it's natural to cry, then holding it back won't do you any good and could do you harm in the long run. If all else fails remember that tomorrow morning the sun will come up just as it has every day for millions of years and that when you open your eyes in the morning you may have moments that don't hurt so much and the same could happen every day.