How to comfort friend and be respectful?

This is actually not a question regarding elder care, but I wasn't sure where else would be suitable to ask such a question, seeing as most people here are faced with really tough issues every day. And this is going to sound horrible. Abominable. I'm not a troll, and I pray I'm not a monster.

My friend married a man who had two daughters already. One has a brain tumor, which has gotten so out of control that she's now blind, and has been on chemo or radiation off and on since she was about four I think. She's almost 10 now. The tumor combined with a cocktail of meds (stuff to keep her from menstruating, stuff for high sodium, high blood pressure, on and on) has left her with a lot of health issues, such as blindness, incontenence (not sure if this is physical or developmental), high blood pressure, high sodium, enlarged heart, etc. She also has severe emotional/ developmental issues-violent outbursts, such as trying to push her father off a cliff while holding his infant son, spraying my friend, her stepmother, in the eyes with various things-febreeze, household cleaner, etc., screaming the "n word" at local shopping malls, theatres, etc., picking fights with kids at school, attacking people, ON AND ON.

They're constantly going to St Jude for more tests, procedures, etc. Needless to say, this baby is just worn out. She can't stop eating, has gained about 30 pounds since Christmas, and has no energy for play.

They've made comments (the parents) about how one day, they expect her older sister to care for her, seeing as she'll probably never be able to be a "functioning" adult.

The reason I'm writing is that they've just found more tumors. In her spine mostly, but more tumors. They're going to check to see if they're malignant as well.

I've tried to support both of them the best I can, but it's hard when I don't understand what they're fighting for. This is what I feel makes me a monster. This little girl is going through hell physically and emotionally every single day for treatment and it often makes her much worse. Her parents know that she'll most likely never have a "normal" life...if she even survives. In fact, a lot of her treatments are just as potentially hazardous as the disease itself. And more painful, from what her stepmother tells me.

It almost seems cruel to me to keep giving her all of these treatments. No, not almost, it DOES seem cruel. But I totally understand the flip side-what else are they to do-let their kid DIE? Of course not-that's cruel as well. I just don't know what's worse. Putting their kid through torment to give her a shot to live a life where she'll be unable to cope or care for herself, or letting her have some stress free years without needles or scans or medicines.

I don't want them to lose their child. I just feel ill every time I hear about a new treatment they're going to do, or how she's losing her hair again, or how they've upped her hormones because her period tried to start again (I think it's a side effect of other medicines), or how they've gone into her head twice now to "whittle" the tumor down (they can't take it all because of where it is).

I keep my opinions about all of this to myself but there's a question that keeps me up at night, and it's one that I fear makes me a monster: What is the point of all this torment on this little girl if they can never "fix" her?