Hi Karen,
I have used a product called Acrylic Medium (Liquitex mediums work great) to make my artist acrylic paints into fabric dye. The Acrylic Medium is a clear liquid product. Acrylic mediums are mixable with water and are heat set with an iron.
I have not tried this yet, but I plan to mix the acrylic medium about half and half with water and spray it onto tea dye or fabric marker on fabric to use as a mordant. I believe this would work well, but please try it on a test piece with your fabric marker first. Lightly spray the liquid onto your markered fabric and heat set it with an iron.
I have fabric that I have dyed with the acrylic paint mixed with the acrylic medium (made into placemats). This fabric has been washed over and over and looks brand new.
Here is a link to some information.
http://www.instructables.com/id/Make...-Fabric-Paint/