Working with synthetic mRNA was hard during my time. I would imagine that it was many times more difficult in the 90's. Just as an EE analogy, working on mRNA in the 90s is like working on extreme UV lithography in the 80s. It was too far into the future to be useful, and there were better research funding opportunities for other things. But if one was smart, one could see the potential. It's not so surprising that she got passed for tenure, working on something so crazy wild. It was around 2005-2010 time frame when mRNA synthesis became affordable enough to become an applied science rather than basic research.
It sounds like Kariko lost her associate professor position in the 90s, but continued her work as a postdoc for more than 10 years. That's some awesome dedication to something that almost nobody thought would work out. It's not so surprising she jumped ship around 2010 when the mRNA tech caught up.
I hope she gets her Nobel prize. She deserves it.