Would this be a good mustang to get for a girl?
I think a better choice for you would be a '67 mustang. It is a smaller car, and still has nice "styling". You could opt for the fastback (example: check the "stangbangers" link below) if you like the fastback style, but I think a girl would look better in the coupe (example: check the "allfordmustangs link below").
The car you have shown is a very large and very powerful car, especially with the performance mods. It would be a difficult car for any "lesser experienced" driver to handle. The smaller Mustangs I have listed (especially with the 289 engine) still have power, but are not as prone to "getting away" from the driver. I'm not trying to knock your driving skills, but if you have limited (or no) experience with performance cars, the '67 would be better for you. The model you are asking about is more of a "road rocket", while the '67 is better to drive if you want a more enjoyable ride in terms of handling and power. Typically, the larger a car is, the more "boat-like" it handles on the road.
I have had the opportunity to either own or share (through marriage) a "few" sports and/or performance cars. One of my favorites was the '68 Karman Ghia (for ex.ee "volkstorque" link below). While not being a "super-powered" musclecar, the response on the accellerator and steering were superb, and you could "feel the road" when you drove. It was a really exciting car to drive. On the other end of the spectrum, was my favorite personal car. It was a 1970 Dodge SuperBee (example: see "forum.avtoindex" link below). It had a 440 engine with a Holley 4160 racing carburetor, which was directly hooked up to the fully functional hood scoops. To give you an idea of how much power this car had, the highway patrol in some states had used them as "interceptors" because they could catch anything that passed them on the road, even if the troopers were pulled over, parked and had the keys out of the ignition. I'd still have it today if I hadn't had to sell it to move out of state and get divorced.
It depends upon what you want the car "for". The '67 is a sporty, powerful car that would probably suit you if you just wanted a cool, fast car. I would strongly recommend that you not get a car with too much power because they can be more than the average person can handle. I could handle the '70 Super Bee, but then again, in my younger years I was also offered the chance to race professionally, because my "skills" were better than most.
I'd be interested to see what you finally end up with.