Well I think Tammi got upset because if Eliz didn't come back, then Tammi wouldn't get the baby she wanted.
The baby broker theory doesn't work for me. I think Tammi was all about getting Gabriel for herself.
I think she applied major pressure to Eliz to come back, and that didn't work for Eliz because she just plain didn't want Logan to get his hands on Gabriel.
I can just see Eliz's fury increasing.
Unfortunately I don't see how she could have found anyone else to 'adopt' Gabriel so quickly (Dec 23 to Dec 26).
I want to know how often Tammi talked to her during that timeframe, and I want to see all the texts between them.
Elizabeth is ultimately responsible, but I think Tammi fanned the flames. I don't see how with Logan's descriptions of Eliz's rages how Tammi could not see the state Eliz was in, and make the quick and easy logical jump to Gabriel being in extreme danger.