well Hortensia is rather posh and not too bad. BUT... and the big but is what it will be shortened to?
There is no way that she will get called Hortensia on an every day basis, so what would you be happy with? Horty? Tensy? Tensia? Hebe?
I do think it's a difficult name to shorten that works well.
My name is Alexandra and everyone call me Alex. I absolutely hate it. Although Alexandra is not unisex- Alex is. Everyone think I'm male until they meet me and is sounds so masculine.
My posh name also now sits very badly with my Irish married name, to the point where I'm actually going to change my Christian name now because it sounds so crap,(I don't want to return to my maiden name though now I have kids).
You need to choose a name that sits well with your surname and any future name she may have.
'Hortensia Williams' or 'Hortensia Elliot' sound fine and quite classically English, but Hortensia O'Leary or plain surnames like Baker, Adams or Rowe just don't go at all.
So I would avoid it even though it's nicer than some and is rather eighteenth century and elegant.
How about something similarly elegant yet easier going and slightly more popular but not common e.g, Clarissa, Georgiana, Henrietta, Julianna, Dorothea, Louisa, etc.