probably less than you think
Women are resilient and fairly good at working out which men are the dangerous ones when out and about on the streets. TBH the level of fear you feel when walking home at night is not connected to the person behind you, there are things we do - in the first situation you described I'd have crossed the road/taken a different route and seen if you followed.
Also, I'd have assumed you would be running not just walking fast if you had bad intentions. She probably thought much the same but wanted to be sure to get inside as soon as possible.
The biggest risk to us is not the man on the street but the man in our homes. That's why I've been single by choice for over a decade; it's a risk I'm not prepared to take. I'd take my chances on the streets.