My doctor prescribed baclfen to me but I don't take it can she test my blood or urine to see if I'm?

If she/he has permission to do so then yes, absolutely she/he can. The drug will cause chemical changes in your body that will show up in the blood and urine so they don't ahve to test for the presence of the drug alone but they can also test to see if the drug is doing what it's supposed to do as well. If it isn't then that'll indicate that you haven't been taking the drug.