I'd have fired her for a number of reasons.
1) An open letter to your CEO is a resignation letter, especially if it is sarcastic, as this one most certainly is. Don;t fire off any form of communication to your CEO unless you are clear what outcome you want and craft your communication accordingly. Calling him an overpaid idiot who is bleeding his employees is never a good message under any circumstances. Poor judgement.
2) She knew what she was getting into. In these days of internet searches - and she certainly found her accommodation somehow - it is inexcusable not to do your homework before accepting a job. I just did a brief search and I found several room shares in female only households for between $480 and $600 a month in Ingleside and Inner Sunset. Not only would that have given her an immediate $650 boost in disposable income it would have taken care of her heating bill and dropped her commute cost from $11.50 a day to $4.50 - that's another $90 boost. The fact that she either couldn't face a room share (prima donna?) or didn't do her homework...poor judgement.
3) The fact that your company doesn't support your sarcastic proposals (I'm assuming) for community outreach isn;t a reason to diss them. How about showing them your success in reducing outflow costs in not immediately giving away cash vouchers? Perhaps that could have become an assessment metric of the team or even allowed Talia to introduce some new training ideas. But she didn't and her tone implies a poor view of her colleagues too. Your ability to improve your job is what gets you noticed and promoted, and its possible that your bad attitude came to the notice of your line management as disruptive. She handled this badly. Poor Judgement
I would call out companies that pay customer facing staff minimum wage as shortsighted. If Talia is right in her assessment of staff turnover then the company is spending a lot of money on recruitment and training rather than staff retention. Benefits are great and there is a real startup/early stage "benefits are all" attitude amongst SV and SF companies. Why not give your staff the choice? I know that health insurance generally costs the company a lot less in a group policy that the market value to the individual, but banking cash is often of more immediate value to low paid staff. Free food is also ok but not as a compensation for salary. Fewer snacks and more $$ drives staff retention. I've never heard of any well paid employee leaving because the snacks weren't up to standard!
So, yes they were right to fire her. Bad attitude and poor judgement do not a good employee make.