Please do not give any more Motrin. Human adult strength Motrin tablets contain 200 mg Ibuprofen. The drug is not safe for dogs. 8 mg/lb/day is a toxic dose. If your dog weighs 10 lbs, the toxic dose is 80 mg, which is less than 1/2 a tab. If she weighs 5 lbs a toxic dose is less than a quarter tab a day. Unless the tablets are marked with a line in the middle to make them easy to split, they should not be split. The drug is not evenly distributed throughout the pill. The split pieces could contain all or none of the drug, or any amount between. Common toxic effects are stomach ulcers, and liver and kidney damage.
Your description of suddenly being unable to stand could be caused by disc disease in the spine (slipped disc), which is common in small dogs. The urination on the floor happens because the dog has urgency to urinate and is too painful and/or is unable to walk properly. This is the most common, but not the only cause of the signs you mentioned.
Is your girl able to walk now? If so, she can wait until tomorrow (Monday) to go to the vet.
If she is not able to walk, is she able to move her back legs/front legs now? If she is not able to move, taking her to an emergency vet would be the best option. Whether or not you can get her to an emergency vet, keep her as comfortable and as quiet as possible. Put her on something absorbent (towel, diapers) if she can not get up to urinate. Offer her water every couple hours and less than normal amounts of food at meal times.
Let me know if you have follow up questions.