Desperately need help housegreaking a three-year old F greyhound !!!?

You need to catch her in the act, tell her NO and get her outside to finish her business. When she does go outside praise her like crazy- make it a big to do when she gets it right. I would go back to tying her to you so she is never out of your sight. It took my 2nd girl a week to figure it out but she got it and has figured out to tell me when she needs to go out.