With telling untruths, I struggle greatly, and i understand this to be a staple experience of autism.
I don't think you need to beat yourself up over it. Kraftiekortie's question is highly relevant.
Depending on the answer, the other thing you you might consider is whether to go to work on your own thoughts. Forgiveness can be as much for your own sake as for the person being forgiven.
Maybe you don't have to forget, but consider whether you should forgive.
Then, one day maybe you could truthfully say it, if she's since earned that.
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"Stress happens. It can be a stimulus for growth. It can plough you under if not offset by rest. I strongly recommend checking out
Peak Performance by Brad Stulberg and Steve Magness,
on Audible."