Can I but my iCloud storage for my girlfriend with my iTunes login

My girlfriend and I have both have iPhones. I straight away upgraded my storage as I knew I need more space. But she thinks she wouldn't need it. Anyhow not that I would say I told u so to her but she does. And her way is deleting apps and photos etc. stuff she uses. So I thought id upgrade her but not tell her.

So the question is! Can I upgrade her account but with I'm iTunes details. Basically want to buy it but for her so. Not using her login to pay for it just mine. Is this possible or is this to far fetched?!

I'm hoping it's not otherwise ill just have to do it the old fashion way and put money into her account and then use hers.

Hope someone knows the answer for my sake and hers of course