Mom is going to get knee replacement surgery but is horrified about deep vein thrombosis. Will the doctor put her on blood thinners to prevent this?

Ask the Surgeon. A great question. There are several variations as to the type of blood thinners to use and the times to use them. Most surgeons have their own reasons for choosing the appropriate one. The specifics can include the type of surgery and the medical condition of the patient. Ask the surgeon this question and I'm sure he/she will be glad to explain their reasoning.