There are two schools of thought: one group (including some fine penmen/calligraphers) says the same fountain pen can be used left or right handed; the second group says that the tines of the nib should bend around to the left, making the last few millimetres of the nib hit the paper at the same angle a right-hander would with an un-bent nib.
Many years ago, Osmiroid made "left handed fountain pen nib units" like that - you can still find them (new old stock) for sale on eBay.
But back to your reason for posting: it depends 100% on whether the person who asked you falls into the first or the second camp. It's a bit like Big-endians versus Little-endians in Gulliver's Travels - you really have to know what the person expects so you don't inadvertently start a holy war. It's probably best to ask them why they think a normal fountain pen won't work.
