Being a male physicist, this is not my area of expertise. So I have to defer to someone more knowledgeable, my wife. It was suggested to me that perhaps the problem is the lip gloss. Maybe your mother should look for a lip gloss that is more waxy vs. greasy. Or perhaps try a product called "lip polish".

Being an experimenter, what I would do is collect a variety of lip glosses of different consistencies and try them out. Ideally, you, your mother, and as many friends that you can gather (to assure an adequate sample group) should try out the different products and see what works best for each person. Perhaps lip chemistry or temperature plays a role. Maybe people with especially hot lips cause inferior lip gloss products to "feather" and "bleed."

By the way, if you search on the scienceline web site(www.scienceline.ucsb.edu) for "lip gloss", you'll find a very good explanation of what lip gloss is.