Always agree a time with her that is half an hour before the time you intend to arrive. In the unlikely event that she arrives before you, just say '1.00? I could have sworn we arranged to meet at 1.30'
Oh, I do sympathise! I lived with it for years with one of my DDs who takes after my MIL. So exasperating!! But they are usually the most delightful people otherwise. Your friend probably thinks that the time to leave her house is the time she is supposed to meet you.
I am sitting here in a coffeeshop waiting for my friend who is already 20mins late! And it's not a one off. I've tried to make myself arrive late when I meet up with her but I just can't do it. She doesn't mean to be late - I just think she underestimates (always!) how long it takes to get ready/travel anywhere. sigh... It used to be just 5 mins, then 10 but most recently it's creeping up to be later and later. She's lovely otherwise so I feel a bit crotchety moaning...