Weddingbee boards

I've been working at the same job for about four years. For the past year or so I've been working with this woman who is in her fifties, lets call her C. She's super caring and for my birthday last year she even bought me chocolate and wonderful chapstick and other stuff. It was super sweet.

On the other hand, however, she is VERY set in her ways, to the point that sometimes she is OCD. I work at Starbucks and she and I often work drive through together. I like her when it isn't rush but sometimes I can't handle her being so uptight. She was recently on vacation for two weeks and it was so wonderful having so much less stress. But this week it's back to the grind. Today I handed her a coffee and I had accidentally filled it a little high. I thought since it wasn't leaking it wasn't a problem but a little spilled out when she handed it out the window and she turned to me and said "Put it in a grande cup!! You should at least make sure to keep 1/4 an inch of room before you put the lid on!!!" 

She also has two daughters who come to visit her. Quite frequently something will be said between them while her daughter sits at the bar and before you know it they're arguing. I mean give me a break! Stop getting in arguements with your 18 yr old daugther at work.

I'm just so sick of her barking at me, panicking about stupid stuff, and in general being an overreactive annoyance. I like how sweet she is, but seriously. I'm not really sure how to get her to view me as her coworker and friend and not her daughter whom she can get into it with. Any ideas?

Does anyone have any adivice? I don't want to be rude but I wish I knew of a simple way to calm her down. Or should I just try to ignore it and move on with my day. I guess I'm one of those people that gets stressed by my surroundings.