Thank you again,
First, these pale gums are a real concern. If we don't have any breathing changes, then they may be telling us that we have internal blood loss or anemia. This could certainly make her weak and unable to hold herself up. Otherwise, she doesn't give me the impression of any issue with her back legs. Instead, that drooling, poor appetite, and refusal to move (usually done to avoid pain) have be concerned about severe gut pain (if there is a blockage from something she had or if the gut is being occluded/compressed by itself or another organ), a stomasch ulcer, pancreatitis, or an issue with the spleen (ie torsion rupture of a mass/hematoma on it, etc). And again if we have anemia, then these more serious issues would be on the top of our list for her.
With this all in mind and again with those pale gums, I would strongly advise having her seen urgently. Her vet can determine if we have active blood loss that needs to be stopped, pinpoint the source of this and her pain to give her the best chance of recovery. At the very least, they can treat with injectable pain relief, anti-nausea treatment, +/- gastroprotectants. But if something is caught or the spleen is compromised, then surgery may be indicated. But in this case, we wouldn't try home treatment here with her signs being advanced despite coming on so quickly.
In this situation, just in case you do wish to see an emergencyvet, you can check @ http://www.vetlocator.com/ or
Please take care,