Funny, I can easily play Kauman's music for mandolin and I don't consider myself advance after 3 1/2 years of playing.
You don't indicate your price range or genre of music played. I have to assume its bluegrass since this is a Bluegrass Forum.
This can make some difference in the sound of the instrument one would like/need. It really doesn't matter in a starter instrument but as you move up in price range, it can be an important factor. An oval hole has good sustain and a good round sound for classical, Italian and Celtic but can't cut through the fiddle and banjo like an F hole in a jam situation i.e., Bluegrass or old-time.
My suggestion is to stay with an A style since you will get more bang for your buck. The F scroll is a nice strap hanger, looks cool , but does nothing to improve the sound and adds a few hundred dollars to the price. I know that most BG mandolin players prefer an F-style because "that is what Bill played" but I'm seeing alot more mandolinist, both professional and jammers, using A's at festivals these days.
I have an Eastman 805 which sounds good, looks good and is an instrument for the intermediate/advance player. The Eastman 505 can be found new for about the same price range as the Fender at $599 street value. The difference between the 805 and 505 is in the add-ons such as binding, tailpiece and fancier wood. For all practical purposes, these items do not add anything to the sound. Unlike the Fender, Eastmans are all handmade, use quality wood and are good sounding.
I've heard that Big Muddy (was Mid-Mo) are good mandolins for the money and in the same $600 price range, new. These are oval hole mandolins but are loud enough to cut through the banjos in most BG jam.
I do recommend that your sister play several first to find one that speaks to her. Don't just limit comparisons to the same price range of mandolin. Have your sister play the more and most expensive mandolins to get an idea of what they sound like. Recently, I had a fun time at Buffalo Bros. in Carlsbad, CA playing all their mandolins (if I had the money, I would have taken home the Collins MT---s-w-e-e-t).
You might want to check for used equipment as others have suggested. As has been commented, $600 will not buy alot of mandolin, it might be better to save up and get something used in the $1500-$2000 range like a used Gibson A-9.
Good luck in your search, let us know what your sister ends up with and how she likes it.
Glenn Nelson
Las Vegas, Nv