Is she close enough you could actually visit? Or is it obvious this would always be an online relationship anyway?

Well she's in a really vulnerable place right now, what with dying and all, so no matter how you go about it, she'll probably feel hurt. Now as others have implied, maybe she's lying to you to get sympathy, in which case, who cares if her feeling are hurt, she shouldn't have lied. But on the chance that she's really dying of cancer, if you want to be nice about it, your choices are either rip the band aid off and tell her next time you talk that you're not really feeling any romantic connection, or give it a week and get to know her a bit and then tell her. If you want to be friends with her while she's still alive, do the latter. If you want to cut off contact completely, rip the band aid off now, get it over with.

You need to buy her a mic and webcam and maybe a smartphone aswell

Yeah if she's being that pushy when you're not interested, it wouldn't be healthy to continue it. You should just get it over with, say you just want to be friends. She seems desperate and lonely, so she might push back, but a relationship just isn't what you want, so be firm and say you just want friendship. Friendzoning someone isn't fun because they're obviously hurt and you don't really want to hurt them, but sometimes you have to. If she doesn't want to be friends, oh well, it would only get messier if you let this go on if she can't handle just being friends. If she does, great, you have someone to hang out with online.

I have read some product views on dating sites an watched some videos discussing that dating sites are a dead end and a complete waste of time.

Online dating is cold, cold approach it is on par with random calling people and trying to sell stuff online or in the past telemarketers, random callers on the phone.
Online dating is a lottery and relies upon pot luck, not skill.

Cold approach in real world is better approach and takes courage.
There are more women on streets at bars, clubs, shopping mall, library, book stores, cafe, etc.
You must chase your dreams and not wait online for something to show up.
There are no top 10 to 20% of guys that get most of the women online that is nonsense line that keeps getting repeated over and over.

If something looks too good to be true it is more than likely a cat fish.
Love Island, Instagram, social media female/male model that lives overseas is not wasting her/his time on a free dating site.
The model pics gets the people to sign up and join the site to make the rich site developers richer as the suckers chase the dream of the perfect woman/man.

Scout by having people find out if someone is interested in you and gather information before making an approach.
More information you have the more likely of getting a better outcome.

Focus on study/career and get some  hobbies/interests and focus on living your life and doing what makes you happy instead of online dating site that leads to nothing but a dead end and lowers self esteem/confidence and may lead to mental health issues.

It won't hurt to start with a sexy, sleek phone, typically of the same make and model of the girl's phone, but Samsung, iPhone, whatever (I'm assuming most phones don't discriminate against one another on the basis of brand); shouldn't matter too much although a more recent model may come off as more impressive to the girl's phone.

Offhand, black phones tend to say "sexy" to girl's phones, but not all phones are discriminating on the basis of color. Maybe that white phone likes other white phones.

Of course, you're really just playing matchmaker to your phone at this point, but in all fairness, what do you got that your phone don't got, assuming your phone falls into the former described above.

Frankly, I'm not even sure why you're flirting with a girl's phone when you can literally go out and buy the same exact phone she has and skip the part where you try to impress someone else's phone with your phone only to convince it that you're more compatible with it.

Lastly, grammar matters.

Send them a dickpic and just wait ;P

Are you really sure she exists,like did she send you a believable picture of her?
The way you are describing it makes the situation look deceiving.

Ask for skypechat with cam.

Don't.
You're just gonna get catfished.

Yikes. Welp, problem solved, for you anyway. Don't worry yourself about it, there's nothing more you can do.