Tina was never unwilling to let her go, she just hadn't confirmed that there were any other plans or issues with school on the Monday (as in today, I believe). She is increasingly worried about Scarlett being 'pushed' by the Thomas clan, but at the same time they've never let it affect the co parenting arrangements. Tina CERTAINLY has an issue with Ryan setting Scarlett up with her own Instagram account though, and the lengths he has gone to get it blue ticked. It's pathetic of Ryan really.
To be fair to Tina I think it says a lot about her that she hasn't made comment about it or held Scarlett back at all, when she'd probably have plenty of grounds to do so.