I can't believe your MIL did that. Well, actually, I *do* believe it, because things like that have happened to us and to so many people I know with food-allergic kiddos. I sincerely hope that MIL has recognized that this is a real issue, and not simply "DIL overreacting."
Since I think dh's extended family is from the region where you are - I've seen that "feed the baby [ice cream, frosting, mashed potatoes, bits of processed cheese, sips of pop, etc.]" sort of behavior with his family - I'm so glad we don't live closer! It wasn't until our most recent visit that I allowed dd1 to be alone with the relatives away from me - because she knows to refuse every. single. food. offered. unless we are with her. Dh is offering that, if you would like, he can tell your MIL what he thinks of her behavior (including lots of
), next time we're in the neighborhood.
It seriously is time for you and for dh to tell family and friends that this is very serious, and that they MUST respect your guidelines with Ellie - tell them, "When in doubt, ask first." And, unfortunately, in my experience, this means that either you or dh (or possibly your 11 year old) ought to be the ones who hold Ellie at gatherings - no one else unless you are right there hovering the entire time. They may think you're a helicopter parent - but they're not the ones dealing with the fall-out if there's a slip-up. Additionally, many people assume that "a little won't hurt," or that small exposures will actually HELP (as in the shots for people with environmental allergies) - all the mainstream articles about carefully controlled medical research on doing just that with peanut-allergic kiddos doesn't help with this either. Remind them that Ellie is not in a carefully controlled medical research group - she is flying solo and doesn't even have an epi-pen at this point!
I'm in tears thinking about how awful this has been. Just when you were starting to hit your stride and feel like you were getting it under control.
Your description of how it happened (from kicking in two hours after the finger-lick to its duration) fits very well with my dd's reactions. FWIW, dd1 was diagnosed with IgE and has an epi-pen for her egg allergy. We never took dd2 to the allergist until she was three, and she had outgrown her allergies by then, but reacted similarly. In the beginning, dd1's reactions took 4 hours to kick in at challenges - at this point, they kick in almost immediately with the projectile vomiting, like clockwork, 2 hours later.
This absolutely is from the icing. No question about it. Nurse away, your milk is not the problem. This isn't in your milk.
In terms of the frosting content - call around to another bakery and ask if they can tell you their individual frosting ingredients (the cake and the frosting are not all from the same box). OR call the bakery again and ask to speak to the manager/owner/baker -- because the frosting mixture has its ingredients on the bag/box in came in (if it came in a bag/box and it seems obvious that it did).
Just guessing, I'd say that the frosting had:
Hydrogenated soybean oil
Powdered sugar (therefore, corn)
Butter (and various versions of butter solids etc.)
Possibly Egg White (very likely, if there were any Royal Icing to it)
...It may also have had some palm oil, guar gum, random other stabilizers. And, if it was a flower or near a flower, it also has all sorts of artificial coloring/dye in it.
For us, dh's family was our most difficult to deal with. My TED and the girls' restrictions were all about the impact on THEM - inconvenient, crazy, ridiculous, all in my head. The only thing that finally got them convinced was dd1's allergist diagnosis, and her epi-pen, and they still slip up. I learned to take it into my own hands - bring a couple safe foods for me/dds to all family meals (offer to make the mashed potatoes or etc.), suggest safe restaurants when we went out to dinner (and never ever mention it was because I knew they were safe, or SIL in particular would refuse to go and want to go somewhere else, learned that the hard way)....
In terms of allergist testing with infants - the tests are less reliable the younger the baby is. You get false positives and false negatives, the gold standard is ingestion. I think if there's an ana response, there will typically be an allergist referral, but many Peds and many allergists prefer to wait 'til kiddos are 2 or preferably 3 before the allergist appointment, so they're more likely to get an accurate test. You could request a referral earlier, you might have luck, but you should be prepared for inconclusive or even negative responses (in other words, don't tell the ILs about it if you don't want them to pooh-pooh your TED if/when the tests say there's no allergy).
Also, I think you're right about the crying from the allergic reaction = increased reflux today equation. We found that happening. Crying with reflux is a vicious cycle.
I hope things straighten out again in the following days!
ETA: Also - I know exactly what you mean about being willing to feed Ellie anything if it means she feels better. At what point dd1 was hospitalized, if the Ped had told us that the only thing that would work for her was bear lard, I'd have found the bear in her den and killed the bear myself if it meant things would get better. It was almost a relief to recognize that feeling - it meant that when we were able to return to breastfeeding, I was doing it because it was what was best for her, not because of me or my wants.