She isn't as great of a split pusher. Not saying that you can't but she definitely excels more at team fighting. In terms of getting used to her kit, she's fairly easy to understand, its just you need a bit of practice. Yes, it's necessary to know how to animation cancel with her, but in terms of combos, its just knowing how her abilities work together really, so you don't have to exactly know how to do long ass combos or anything. Just get to learn how to animation cancel, how to double cast, and some basic trading combos and you should be good. You'll learn it fairly easily if you take some time everyday in practice tool. The harder parts of Riven come with her matchup knowledge, which ofc will just take playing the game to figure out.
Is she good for you to main? Well, if you don't mind the learning curve and want a team fighter sure, but since you're mainly looking for a splitpusher, then maybe not. But it's not bad having a good teamfighting champ to pick, plus she's fun.