35 y/o and diagnosed with HER2 positive breast Cancer

I had a her+ cancer but much older than you.
My niece was your age though and she had 10 positive nodes. She was on the herceptin trial and 16 years on she is cancer free. Her babies are all grown. So lovely there is wonderful treatment options for Her2+ cancers now.
You can do this. No more blame..future focus as you need your energy for this.