I don't know how to deal with friendship conflicts

I gave a extremely simple job with my friend. All she ahd to do is to be mindful of time because I have to do something but I'll be back. I pay her more than her previous, which mean a win-win situation for us.

However this friend priotize her boyfriend's request during the working hours. In short, she forgot to do the job.

Later on, the client hated me because of what happened. Now, I have a bad record after building my reputation to that client for 2 years.