Many years ago, I had a good friend who, like me, was divorced and had 2 little boys. Our children were about the same ages, and all was well. Then I met a man who became my 2nd husband and she was a maid of honour at our wedding. I was soon pregnant and my friend visited me while I was in hospital. (I'd had a Caesarean and they kept us in for a week in those days).
Unfortunately I was asleep, so rather than disturb me, she left a card and a gift, which the nurses gave me when I woke up.
I responded by sending a thank you card, but never heard from her again.
I phoned her several times but she never answered. I left messages, I wrote letters - I was getting really anxious - and I called in at her house, but all to no avail. The ten years later I bumped into her at a charity event, and she acted as though nothing had happened.
I totally understand the AcornFairy's pain and distress, but unfortunately, I don't think there's anything to be done, regardless of whether her friend or the husband is at the root of all this.
Let go, grieve and move on would be my advice.