I would involve her in the decision about diapers. For instance she may have views regarding things like perfumes and chemicals. Who knows, she might even have a preference for cloth over disposable. There is no reason why not to ask her. She will appreciate the kind gift regardless whether she knows or doesn't know about it anyway.

I myself insisted on using cloth. The best gift of all those I got was a year long membership to a professional diaper service.

The second best gift I got was a car seat which several friends combined together to purchase.