As a lefty, pistol type will play a factor depending what you/she wants. Often, learning from the start to use a certain pistol that is missing some of the controls on the right side is not a factor for a lefty, but can be for a right handed person trying to teach a lefty to do it left handed! As Shawn mentioned, if it has a thumb safety then that is about the only thing that needs to be on the right side of the pistol. A slide catch is second place, but most lefties can easily learn to lock a slide open using their left pointing finger. As far as mag releases go, I used to flip them over to the right side for thumb activation, but with smaller hands it is actually easier to have the release on the finger side for easier use. Again, something a right handed person with larger hands would not understand.
Now for gun choices you should think about what feels good and what performance level you want as you could end up going through a number of pistols before you are satisfied. If you really want to keep it simple a striker fire pistol is a very good choice. The PPQ has a lot of good reviews. I have an M&P Pro Core and enjoy using it. With an Apex trigger it is one of the best shooters I have. I had a Girsan (B92 clone) that was good, but I quickly outgrew the decocker style of pistol. The CZ Shadow I owned was another good choice and was very left handed friendly. It fits most hands, but may feel heavy until the shooter realizes how smooth it shoots. Most 1911s in a single stack would be OK, but depending on the grip they could be too large. I know my double stack 2011s are all large grips, even the small ones.
My best advice is to get softer loaded 9mm ammo to start with, depending on what your/her intentions are.
