Discoloured Acrylic - have you ever come across this before???

[Bev Rose]

Now just thinking out loud here, is your UV top coat porus? (soak off not buff off) if its not a buff off top coat (or gel top coat) u will see colour change like this from garments....

infact you should see a dramatic colour change this time if the dressing gown is the offender since you have hand buffed the enhacement this time (full porus surface)

Do you have any Brisa hun? you could cap her nails with UV top gloss (making the surface chemical resistant ie non porus) just until the dressing gowns had enough washes to get that ink out.

alternatively if the dressing gown wont stop bleeding ink she can get fabric colour sealants to wash it with

Had this happen to me with a pair of new ink wash jeans damn things would turn my nails grey lol

I do cap her nails with a UV top coat (non porous) normally - Star Nails GF21 UV top coat.(as 1st pic)
I've never had any probs with it discolouring on it's own - it usually needs the usual subjects like curry (turmeric colouring), fake tan, sunbed etc. But non of these apply to her.