Yellen is an old bitch (a female dog) so it is understandable if she can hardly learn new tricks. Not to mention that she's been fully immersed in the system for decades. But she's probably fully aware that despite her reservations against crypto, the American people are very much into it and that even leaders are aware of its potentials. Some are already embracing it. So she's probably not that close-minded as to immediately dismiss any explanation in favor of crypto.
I think pretty much the same. For starters, I don't trust Yellen or anyone else who has held as many positions of power for as long as she has. I think if she makes those statements it is because it suits her in some way, and surely, as you say, they are putting into practice the, "if you can't beat 'em, join 'em."
As I have said in other threads, in the beginning the reaction of governments against Bitcoin was negative, but now they have realized that they can't stop it. What they have done, then, is to pass legislation to control it to some extent.
According to statista, as of today 15% of Americans own cryptocurrency. And the trend is growing. Although I would take this kind of statistics with a grain of salt, I think it is true that a significant portion of growing own crypto voters and the policies regarding it will influence their vote.