The good news is strokes are not at all common in dogs. You can read about them here
an inner ear condition can cause wobbling and lack of rear control and you can read about this here
sometimes you see an obvious external ear infection with this and sometimes not and though its seen more in older dogs it can still happen in younger ones with inner ear infections.
Dogs can also injure their spine. One possibility with a sudden onset is a fibrocartilaginous embolism
and another is an intervertebral disc problem
I'd keep her quiet and plan to see your vet when you can.
If she gets worse then this site may help you locate an emergency vet if you need one
Hope this helps you!