To her dismay, Tina had to wait because I went inside.
Why did she have to wait?
I had something important to take care of.
If you knew you needed to run an important errand, you should have considered rescheduling your meeting with Tina for a day when you were not so busy.
She should have expected it, as I told her it would take time.
Even if she expected it, it's not okay to make someone wait for long periods of time.