My guess is that Pelosi knows this whole impeachment thing is a complete loser. You know she is probably beyond pissed that they started this to begin with, it was clear she was against this (not because of ethics or anything like that, but she has been around long enough to know it was a really stupid political move). But AOC and others created enough talk of it, that she had to go through with it.
Pelosi is probably thinking, lets just go ahead and go on with this and have it fail. The sooner that happens, the further we can distance this failure from the upcoming election and by then, they can find a new thing to call Trump Hitler on.