Hi,
Unfortunately, I can’t comment on the Siff Saff as I’ve never played one.
When I first started the harp, I rented an Teifi Eos from https://affairsoftheharp.com from a lovely woman in Leeds for about a year whilst I was waiting for my mine to be built. When I did have face-to-face lessons pre-Covid it was on an Aoyoma, The things that I found to be different were that the strings were closer together and the tension (i.e. how hard you have to play the string to get the same level of sound) less. The thing I like about the Eos is that the spacing and tension is the same as on a concert/pedal harp, even though it is a lever (non-pedal) harp so that when I progress over the next few years and I eventually want/upgrade to a pedal harp, the transition with regard to playing will be easier (apart from sheer size and having pedals!).
Also, different harps suit different people. As an adult learner with adult hands the Eos suits me perfectly. An Aoyama may suit your daughter/child for now but her harp teacher will be best able to advise on this. I think the important thing is that she has a harp for regular practice regardless of size/type as long as it works for her.
There is an Aoyama to rent here https://affairsoftheharp.com/harps-for-sale-hire/ and there are other schemes that rent, such as https://teifiharps.com/harp-hire/ and https://affairsoftheharp.com/harps-for-sale-hire/ which uses the money you pay for renting towards the cost of owning your own.
Others:
https://www.handsonharps.com/our-harps/
http://www.pilgrimharps.co.uk/second-hand-harps.html
https://derwent-harps.myshopify.com
https://hobgoblin.com/fretted-amp-stringed/harps
http://www.thomasharps.co.uk
https://www.promenademusic.co.uk/Harps
and I am sure there are many many others out there, too.
However, always ask a harp teacher based on your daughters needs as different people need different things depending on their stage of learning.
Hope that helps!