"In addition, the viruses that cause mono (see Mononucleosis Causes) can be spread in other ways, such as sipping from the same straw or glass as an infected person, or even just being close when the person coughs or sneezes. Also, some people can have the virus in their systems without ever having mono symptoms, and you can still catch it from them.
For this reason, transmission of mono is almost impossible to prevent; therefore, no special precautions are necessary for someone who has mono in order to prevent the spread of the illness."
Better to let her know now so that it can be caught and treatment can start so you'll feel better! Take care! :-)
I just got over mono. My boyfriend and I both got it. When I started to feel really bad, I just told my mom my symptoms and asked if she could take me to the doctor. If it's positive, ask the doctor how you can get it. There are many ways you can get it and if she hears it from a doctor, I doubt your mom will assume its from kissing. Good luck, and hope you feel better!