Ask Mr. Smarty Plants

That beautiful name does sound like it should be shared by a lovely flower, but no genus, species, subspecies, or varietal name like that currently exists, according to the International Plant Names Index, a standard reference for looking up scientific plant names.

It seems more likely that a horticultural cultivar would receive an evocative female name, and we did find a mention in an academic journal of a German cultivar of winter rapeseed called Brassica napus ssp. oleifera 'Orabel'. Rapeseed is a plant in the mustard family from which we get canola oil. Unfortunately, the journal only mentioned it in passing as part of a list of German rapeseed cultivars. There was no picture of it and we haven't found more information about it, but it wasn't bred for looks so I doubt it's what you had in mind.

My guess is that there may well have been ornamental cultivars with the name 'Orabelle' or 'Orabel' in the nineteenth century, when those names were more common than they are now. Finding records of that could be daunting, as various kinds of cultivated plants have their own International Cultivar Registration Authority organizations through which new cultivars are registered. It might take contacting some of these Registration Authorities to find out if any cultivars ever carried your mother's name.

For more on plant naming conventions, see this summary.