Whom does Daisy love? Is she capable of loving anyone? Why?When Tom and Gatsby engage in an argument and confront each other, they make Daisy...

I see the issues involved in answering your questions a
little differently.  I don't think how Gatsby made his money has anything to do with
Daisy's ultimate rejection of him.  It may be a bit of a stumbling block, but it's not
that much of a problem.  I don't think Daisy cares how Gatsby made his money.  It's too
far removed from her.  She cares about maintaining the status quo, and about
respectability, to a certain extent.  But the issue isn't
major. 

I give Daisy more credit that some commentators
do.  I believe the reason she rejects Gatsby is because she does have a sense of
ethics.  Not in terms of how Gatsby makes his money--again, that's too far removed.  She
accepts that just as most readers do--look how famous Al Capone is.  On the surface,
bootlegging is often thought of as a victimless crime.  The government was the foolish
force behind prohibition, and therefore bootlegging.  The government was in error. 
Haven't we allowed alcohol production and sales ever
since?

Daisy's sense of ethics comes into play because, as
she herself says, Gatsby asks too much.  Gatsby insists that Daisy pronounce that she
never ever loved Tom; that she always loved Gatsby.  That's how Gatsby loved her.  And
he insists that Daisy recipricate, that she say that she loved Gatsby the way Gatsby
loved her.  And Daisy refuses to do that. 

She does it at
first.  Her initial reaction is to agree with Gatsby.  She is upset with Tom and knows
he's been having an affair.  (And please note that this is after Tom accuses Gatsby of
bootlegging.)  But the second Tom shows a little tenderness, and reminds her of some of
the tender moments they've had together, she recants and tells Gatsby that he asks too
much, and sides with Tom.  She refuses to perjure herself.  She did love Tom once, and
she refuses to say otherwise. 

She refuses to take part in
Gatsby's illusion.  He idealizes their past relationship and his illusion is dependent
upon Daisy loving him as much as he loved her.  And that just isn't
true. 

Think of it this way:  Gatsby has as much money, or
even more money, than Tom does.  Who has the nicer shirts?  If money were the issue,
Daisy would side with Gatsby.  But money isn't the issue.  Daisy sides with Tom because
Gatsby asks too much.

Finally, does Daisy love her
daughter?  We don't really know.  All we know is that Daisy feels sorry for her
daughter, because her daughter is a female born into a male-dominated world.  She will
face the same crummy situation that Daisy faced:  her only chance for social and
economic improvement is to be a pretty, little fool, and marry a wealthy
man.