Sorry that you've now found out it is lichen planus,
@Irish Maeve, I will ask my sister which mouthwash she has been prescribed & also the toothpaste she now uses. She actually couldn't use anything to clean her teeth before as any set her mouth on fire & the 'webbing' got worse. She has been reading lots online & went through the meds she takes, she found that Metformin could trigger it, so she stopped taking it & thankfully has found some improvement. Anyway, I'll post up the names of the two things
tomorrow later, once I've spoken to her.