The buffs sound reasonable.
I like playing Sivir, Miss Fortune, Jinx and Kindred (sometimes in ADC position) but Sivir really loses a lot of matchups early and mid game. There's just too much bullying in lanes and even though she can prevent one crucial initiation on top of her, this safety doesn't really guarantee the upper hand for her.
I also reckon that her AA range should be slightly increased when Richochet is in use by 25 units. This allows for a very specific buff when her Richochet is active as it already gives her AS and would help get off damage faster in fights with other champions or allow for faster waveclears without giving her permanent safety net by giving her AAs 25 range permanently.
All in all, with enough items as Sivir, she isn't bad at all but the point right now is getting to that point of having those items. If you're just always getting bullied in lane, you are always struggling to reach the point where she's strong enough while every other champion outclasses her and is ready to fight sooner.
I've heard that some people also think that she needs a new passive but i don't really know about that. Her passive is meant to catch up to people she's chasing and landing her AAs but with how weak she is early, her passive isn't really being utilized until the late game and even then, fights are over in a few hits from either side. I think that with fixing Sivir's early and mid game would go a long way of making her passive feel more satisfying rather then giving her a new one.
#EDIT:
I would also like the option to recall her Q like Draven can do for his ult, which would allow Sivir to control the area she is fighting in. Her Q getting recalled as soon as it hits a champion would actually be a nerf as it would help her in 1v1s but would suck for sniping for kills and hitting the front liner that's blocking for their teammate. So allowing Sivir to decide its range would be a lot better option, in my opinion.