What should you do with off meta things like AP Riven?

I wanted to make this post a while ago, but I forgot or stuff happened, I don't really know.

Anyways I had an AP Riven on my team, who after like 35 minutes realized how useless she was with just a Lichbane and Ludens to deal magic damage, and bought AD items. But until then, she went negative and felt like a heavy weight.

I didn't even care that she was negative cause she was decent at Riven, or decent from what I've seen of Rivens, and we were doing okay in the game. But the fact he/she went AP Riven was upsetting.

So is this acceptable? Because AP Riven is a new level of off meta than. Its not even like AD Janna, because at least your auto's scale with AD. It's not like Nautilus mid, because you can still lane and do all your stuff it just might be harder. AP Riven might as well have bought no items except a sheen and occasional Luden's proc that were empowered by the AP she did buy.

I dunno if there is a clear answer, but it'd be nice to know how I should react and handle this. I don't think its reportable, but maybe it is griefing or giving up?