I do not believe Pelosi would do this unless she felt she had Ironclad evidence. Hip hip hooray![nbcnews.com]pelosi-to-announce-formal-impeachment-inquiry-of-trump-69765701894
I think Trump was being so blatant about actually saying he broke the law and didn’t care (again) she had no choice.
She picks her fights carefully and usually has all the verified information she needs to make her decisions.