I don't know Heidi or Christina at all, I'm not in the HP fandom, and I'm not taking sides here -- but what I see from Christina's comment and Heidi's reply is a genuine misunderstanding. Christina's very obviously trying to be polite, and her deferential polite language puts her actual concrete request (to post the Amazon link) in the middle of the second comment. Her first comment is an explanation of her need for the link to be posted - but it contains a paragraph that does look like she's asking Heidi to organise something with her real life charity contacts. By talking about Heidi's wide range of "contacts" in a comment to a post in which Heidi is talking about just such a real life contact's charity work, I can see where the misunderstanding came up. It looks like she's asking for a number of things: for some sort of educational campaign on her terrible illness, for that information to be spread on LJ, and for her Amazon link to be posted.

Given that Heidi went to some trouble to direct Christina to what she thought was a more helpful LJ community, offered to alert her friendslist to Christina's post there and said she'd use the Amazon link, I don't think it's fair to say Heidi didn't want to post a link. She misread what Christina was asking, but I think Christina then misread Heidi's "refusal" - the only thing Heidi said she couldn't do was something Christina didn't mean to ask for, but the refusal was read as being for the action Christina did ask for - even though Heidi had offered to do what she wanted.

I think both of them misread each other, both are under medical stresses, and neither deserve to be made targets.