You mentioned paying the ETF of ~$100 as a possible option. I assume your plan was to use a dumb phone for 2-3 months instead? Couldn't you just use a dumb phone for the next few months and pay the data fee instead? Surely it'll be cheaper to pay $30 for 3 months than $110 now?
If she switches to a dumb phone for a few months, I don't believe that she has to pay the data fee. She could pick the cheapest plan available for that phone. Data is not required on those phones and I don't think that she will be tied to the data package.