How do I repair trust in a business relationship?

I sent an invoice with a price increase to a client that I have a very close working relationship with.
She was quite angry and hurt, not because of the money, but because I didn’t discuss it with her first.
We have worked together daily for 9 months and there was no excuse for me not to have brought it up before I sent the invoice.
I had taken the advice of others, when I knew I should have spoken to her about it first. It’s the first time I have ever increased my price and I was really nervous and unsure, even though I know it was a reasonable increase.
I don’t want to damage our relationship, but I don’t know how to go forward from here. I have apologised, but there is so much tension and it’s awkward to work together.