CG - I feel your pain! My male lab has been battling something for a couple years now....been under control with meds, but this morning when I got up, he couldn't get his back legs under him and he kept falling over. I increased his meds today and now he seems to be doing much better, but I know it won't be much longer before the meds don't have an effect anymore! Dreading that day!
I agree with dgman on taking her to the vet to put her down. Much more humane! I've had to do it the other before, and it was waaay harder!
Do what you know in your heart is best --- Good luck!