It really wasn't and I'm going to guess you haven't actually watched it and had this post lined up regardless. She was against a host who basically didn't want to let her speak or get her arguments across but she still managed it and made him look stupid quite a few times.
The interviewer pressed her for precision. She handled that reasonably well, however she allowed herself to be talked down to and that wasn't a great look; then she attempted to deal with that but looked ragged doing it. I know that can be interpreted as a gender bias analysis and one based on tone, but it really isn't. On the issues she looked ropey...
There was a lot of errors in there: not fully endorsing the trans issue in prisons but merely stating it's a legal requirement and that she'll go along with it; a half-arsed attempt to distance herself from Biden's four years in office; struggling badly on the border questioning she was getting and pretty much agreeing - ridiculously - the situation is not one to be proud of; waffled badly on defending her own record as VP.
I watched the CNN panel afterward and there was pretty much agreement that 'she was strong' but that the interview wasn't great.
Again, I want Trump beaten, but Harris and Walz look like a weak ticket to me. This should have been a slam dunk once Biden was out the way; any competent Democratic ticket - and one with a massive warchest dwarfing Trumps - should have galloped into the distance and away from that lunatic. As it is it's still a toss up.