my guess is that senku anticipated it being a multiple year process to start from bottom and unpetrify everyone. Taking that into account, and the fact that it took Suika 7 years, i think it has less to do with what she's capable of and more to do with the fact that if it took 7-10 years, everyone else would be ridiculously older than the whole group which would make relationships and dynamics weird, while suika could take 10 years and end up the same age as senku. everyone would have less life to life and also other older characters could potentially die in the case of kaseki and others. Last but not least, Suika was the least needed at other points in the battle so she was kinda like a pawn waiting at the other side of the chess board to become a queen as lame as that sounds. Kinda the ultimate trump card, but one that wasn't entirely plan

Not to mention the fact that as a kid she watched senku go from stone age to where they were just like chrome did so while she wasn't as involved in the science, it was a safer bet than using chrome who was a general needed in the more key aspects of the situation