Bayonetta is a bait and punish character, but that's not as hard as it sounds. Playing defensively unless you absolutely have to maximizes the chances of finding an opening on the opponent. If you notice the opponent is landing unsafely or whiffs an attack you can use heel slide to go get a starter. If they're approaching from the air you can crouch and make yourself hard to hit, then utilt or dtilt to smack them again. If neither of those are working, throw them in the air and make them land. It's pretty difficult to land a raw utilt or dtilt on a smart opponent, obviously they don't wanna get hit by those, however the aforementioned landing catches as well as smart perfect shielding or reads of what their next move will be can make it significantly easier. That's about all I can think of now, but feel free to ask more if you need pointers.
Meanwhile, her strings that can zero death are pretty varied. Ultimately most of the true 0-deaths can be escaped thanks to a lack of hitstun or good DI/SDI. If you want something to true 0-death, the string should probably start with some normal combos so the opponent gets to a suitably high % that they can't escape and also get launched high enough for a move to kill. Fair combos off the side (dtilt>fair1>up b>dj fair1>up b>fair123 etc.) can kill at close to 0 but can be escaped by most characters. Any combination of fair>nair, fair uair, dtilt bair uair, utilt bair, utilt uair, and anything else can lead into a lot of % perfect for setting that up. Ultimately, however, if the opponent knows how to SDI or DI it will be very difficult to kill them with a combo sans getting a single hit up b. Still, keep trying, and a lot of this stuff will come with experience.
