Is Chell an android?
No, I doubt it. Regarding the first two, in the training chamber you go through, Glados states that the normal Chamber 16 is down for maintenance, so Chell instead is put through a training course for military androids (which is why there are so many turrets in there.) Those lines are simply her trying to manipulate the androids that normally navigate said chambers.
As far as the last couple go, the Moon Rock gel probably didn't kill Cave johnson in a single day. It's more likely prolonged exposure that gave him said poisoning. The repulsion gel is a bit less clear, but perhaps it was a prototype version that "does not like the human skeleton", or maybe Chell's somehow immune to it. For example, IIRC we know Chell's the only one out of however many humans put into stasis to actually survive, she's not exactly an ordinary test subject. It's not completely explained, but there's various possibilities.
Finally, there's plenty of things Glados says that point to Chell being human. For example, she was put into stasis like a human, and certain comments (like the ones about her being fat or Glados mocking her about being an orphan) just wouldn't make sense if she was an android. Not to mention, I believe that in the one room with the various potato batteries children made in Portal 2, one of them is marked as Chell's, which would undoubtably prove she's just a normal human. So, long story short, there's no real reason to believe Chell's an android, and plenty of evidence to the contrary.
And one more point that I almost forgot.
What kind of android can eat cake?
Chell is probably not an android.
The first two mentions of androids ("Well done android" and the reference to Android Hell) are probably not there because she is an android, and more likely because that test chamber is the "live fire course for military androids" and GlaDOS is saying the lines she would say to actual androids that were made to run the course.
Chell probably says nothing because she is a silent protagonist, like Gordon Freeman, whose Half Life games take place in the same universe as the portal games. In addition, Atlas and P-Body are not silent; they make noises when you make gestures and possibly at other times.
Chell is most likely an orphan because GlaDOS killed her parents. In Portal 2, in the room in which you first see potatoes in that game, the project with the potato that has grown freakishly large is signed by Chell, as shown in the screenshot following this paragraph. This matches with the theory on the Half Life wiki that she was visiting Aperture Science for Bring Your Daughter to Work Day when GlaDOS took over, and that Chell was among those GlaDOS trapped there.
The fact that the gel does not harm Chell can then be best explained by gameplay-story segregation. This is evidence that she may not be a normal human, but all of the other evidence points to her being a human. Also, as Nicholas pointed out, Cave Johnson died due to prolonged exposure to the Moon Rock Gel, and even with the significant exposure Chell has, the game is not long enough to see what long term effect it actually has on her.