Here is what Toki is trying to prevent.

If she travels before the she summon the 1st Millhouse, past Toki fix the Fluxometer and "enjoy" a virgin life in one of the dullest meta I've ever seen in Hearthstone. Desperate to escape this doomed existence she eventually fuck up the timeline (figuratively) and that's how Infinite Toki is born.

Or maybe she just wanted to have her fun time with Millhouse, this is fine too.