The Sigma isn't their finest gun, but I've found them accurate and reliable despite the terrible trigger noted above.
Steer well clear of Taurus. While they can make a decent gun, they also make many that are very bad.
I'd suggest she go with a S&W M&P (C) in 9mm. Great pistols at a very reasonable price point.
9mm is much smoother to shoot and with today's high tech jhp ammo just as effective as .40 S&W for SD purposes.