Did something urgent cropped up the last minute? One time is possible, but having it happened three times is a stretch. Or she is too busy? What I could deduce from this is the other party is in no hurry to settle the issue.
You must have the same experience before. Your friend calling you to inform that she cannot make it for the dinner as her baby is sick. Your colleague postponing the meeting because the boss needs to meet an important client flying off today. Your customer rescheduling your appointment because his office needs to rush out some urgent delivery.
After all, taking care of her sick baby is more important than having dinner with you. Meeting the important client is more important as it's easier to reschedule the internal meeting. Making money is more important than meeting you, unless it's a sales opportunity.
What if you've arranged all your activities and place to accommodate the appointment only to find out the last minute that the other party cannot make it. You rescheduled the meeting this morning so that you have ample to travel to your appointment venue. You'll need to arrange your coaching session with your staff in the evening instead of the planned time. Your proposal can only be submitted tomorrow instead of today as you need to work through the night. Now you got to re-arrange everything and it's not going to be easy as others already have their plans. It's not only frustrating but also sapped the energy out of you.
And ever so common is being late for an appointment. 5 to 10 minutes is acceptable. But imagine late for a good 15 to 20 minutes or even more.
Many of us take rescheduling and postponement of appointments and being late for appointments as part and parcel of life, especially toward your customers.
There are valid reasons like the ones mentioned above. They could also be intentional. Some people are late for appointment to show that they are more important. Some people postpone appointments all the times to tell others that they are not desperate for the deal. We call that play hard to get.
For reasons that are intentional, there's nothing you can do except to stop playing along with them in their mind games. The more you accommodate their behavior, the more kick they get out of it. It is difficult to do it especially if the client is your biggest customer. But sometimes you have to put your point across there's a limit to how much you can tolerate. You have to educate your client to respect your time.
Likewise for you, keep to your appointment if you've agreed to it (bearing unforeseen circumstances). And don't be late. You have to respect the other party's time.