Days before, she had been given a police warning for harassing Mr van Dongen's partner, Violet Farquharson, 46.
Wallace, described as controlling, jealous and vindictive, attacked the engineer at her flat in Westbury Park, Bristol.
Consultants agreed to it and on January 2 previous year he died from a catheter inserted into his heart.
But the court heard that Wallace was fascinated by acid attacks, had viewed more than 40 websites about the substance used in the lead-up to the attack, and had deleted 82 from her browser history.
Speaking outside the court, Mr van Dongen's father Cornelius van Dongen paid tribute to his son and "best friend". 'She laughed and just threw the acid. I hope that Mark can now rest in peace.
He said: In her darker moments, she bought a bottle of sulphuric acid.
Wallace claimed she thought she was throwing a glass of water over van Dongen.
Arriving at hospital, Mr van Dongen's injuries were so severe he was initially only able to communicate by sticking his tongue out.
Det Insp Paul Catton of Avon and Somerset Police said: 'While the jury has concluded Wallace's actions did not amount to murder, we felt it was the right thing to do to ask them to consider the charge'.
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They want to speak with anyone who may have had contact with April Carpenter in the time she was reported missing. Her family members say they believe April Carpenter's death is suspicious because she loved life and her family.