I don't think you'll need a balanced line out if you're just playing small rooms acoustically. That's for bands who need to run their amps into the PA. I don't see that happening with you so you could likely skip it. A lot of practice amps do have inputs for ipod and headphones...some don't. The BA108 is one that does. I never tried it but it does have it.
And as for cables, just get a decent $15 20 footer and you're set. You don't need a special "bass" cable, you don't need to spend $50 on a cable...just get a decent $15 one and you're fine. I don't think I've spent more than that on a 20 ft cable in my life.
+1 on cables. I've had very few cable failures in my life. Never the less, I always carry a few in my gig bag. 10-15$ is a fair price per cable. Under 10 though it is either a really good deal or a really cheap cable.
On the DI, it isn't just for PA. I did a little live studio "concert" recently on a radio show and the DI on my Genz Shuttle 6 came in very handy for that, as the studio only had one instrument DI available (which was used by the acoustic / electric guitar). I was sure glad I had it with me.
Jill, as to your question on the
Balanced LIne Out (or DI) , it is a "direct input" jack for connecting your signal directly to the mixer (PA or otherwise) without having to mic the cabinet. It uses a balanced xlr mic cable to connect you directly with the right signal level for the cleanest sound. Having this on your amp instead of going direct into the board (via a stand alone DI or a board with an instrument level input) allows you to have a monitor next to you which you are familiar with and which you have instant control over (without affecting the audience's mix in the PA). That said, you can certainly live without it and it isn't a deal breaker at any price level, more of a "nice to have" once in a while. Many have a pre/post switch which determines if your signal is direct from your instrument with no EQ or after your EQ section on your amp.
As for the aux in and headphone out, here's a quick run down of a few of the recommendations:
Model___________Headphone_________Aux In
Acoustic B100..........No......................No
Ampeg BA-108.........Yes.....................Yes
Ampeg BA-110.........Yes.....................Yes
Carvin MB10............Yes......................No
GK MB112...............Yes.....................Yes
Line6 Studio110.......Yes.....................Yes
SWR LA110.............Yes.....................Yes
BTW, I use my aux in regularly for practice. It is a very handy feature. The headphone jack obviously makes it a cinch to practice any time day or night.
) of the GK under these circumstances and in comparison to the other choices even if her situation were to change she would have more wiggle room. 
