its hard to admit but i have spoken quite harshly to my bubba at times! even swearing!!! admittedly not out at the shops, but mainly at home when she WON'T sleep! does that make me a bad mother? probably! i say to myself i wont do that when she is older, she cant understand at the moment....... what do you girls do when you have that angry, frustrated, tired, feeling? (not that i do it all the time, just at the extreme)
I hear you well, I had two reflux babies that rarely slept and know the frustration you talk about.

Best thing to do, is go where you can't hear your baby for 5 minutes and take some deep breaths. Make sure the baby is in a spot where it's safe to leave her alone for a few mintues, ie, cot. Do this when you feel like you are getting to that swearing/harsh point. It really works well, and the baby crying for a short period of time isn't going to hurt it, it's much better for her to clear your head for a few minutes so you can go back in and deal with the situation calmly. That brought me from the point of anger at baby, to going back feeling sorry for and mothery/nuturing to the baby, just that minute or two of time out for me.