Don't they go to births with other doulas before starting by themselves? I wouldn't want someone who hasn't been to a birth or given birth trying to suggest positions and things. When I'm in labourland I need someone I can 100% trust and that means having experience. Your DH is right - he has more experience than she does.

People have to start somewhere. I'd just feel more comfortable if she was learning with someone first.

On the other hand, she's not there to replace the medicos. I had an IM so no experience with doulas. Just make sure she's sticking to her brief - encouraging, helping you stay focussed and not getting in the way of things.