As a landlord, I wouldn't do this. I would want the white goods to be in my name (if I had agreed to provide white goods as part of the tenancy, of course) so that I own them. If she buys them, you don't really have any proof that you own them and there would be nothing to stop them taking them when they leave. Remember to update your itinerary with the new items including make and model number (and I include photos but I am extremely thorough with this kind of thing).
I also don't understand why you allowed her to dictate exactly what type of oven/washing machine she wanted? I'm sorry but that is not her place. You are buying goods for your property and her needs may not suit the next tenant, or your own preference for brand, type etc. In the long-term scheme of things, it is still your property and for all you know she might only be there for a short time, leave, and then you are lumbered with white goods that you might not have chosen yourself (e.g., a brand that is prone to breakages or being unreliable).
When the oven broke a couple of years ago in my rental property, I chose one that was suitable for my budget etc and paid slightly extra for a Sunday delivery that would be more convenient for the tenant. However, if they said they couldn't be there, I would have gone over myself (I know that is not very convenient in your case).
I really wouldn't start allowing the tenant to choose things, do maintenance and take it out of the rent. This seems too casual an arrangement to me and I would want full control over what was bought, who did the work, why and when etc. At the end of the day, property management company or not, you are the one who is liable for ensuring the property is safe, meets fire regulations etc, not the tenant and you don't know how sensible/knowledgeable they are about this type of thing.
By the way, I know you live a long way from the property but I manage my rental myself - the estate agents are almost always rubbish anyway so it seems like money for nothing. Maybe you could bear that in mind for the future and consider that as a possibility?