Sorry if this has been suggested already - I've just skimmed through the posts... but did you say you got AF yourself a few days ago? Just another thought to throw into the mix:

I'm sure you know that women who live together often end up with their menstrual cycles in sync due to the influence of pheromones. In my experience, some women can have a HUGE influence on others - eg. if I spend more than a few hours with one particular friend of mine and she is pre-menstrual, it can throw my whole (usually very regular) cycle out. If it is AF, I wonder if it's just a little bleed triggered by the presence of your hormones / pheromones, rather than something established by her own maturation - just a theory??

Obviously this requires lots more investigation (than my stab-in-the-dark theories) and I really hope you get some clear and comforting answers very soon. Hugs to you.

That also crossed my mind.

Unfortunately I only have black liners, so they aren't any good...
I did tell her she might need to be looked at, she's emarrassed, but ok with it iykwim.