For me, your second interpretation describes the actual meaning of the sentence much better than the first. However, you have skipped the "vielleicht". That's why @Janka wrote "there's a may missing" - if we slot it in, we get: "you may have made her all the more convinced that ..."
Where I'm not quite sure is the first part of your sentence 2.:
You have translated "Wenn du es getan hast ..." into "By doing that ..."
Again - for me, personally - it should be: "If you have done it, ..."
Cobbling it all together, you could write:
"If you have done it, you may made her all the more convinced that ..."
I still don't like this translation eg the meaning of "convinced" is closer to "überzeugt" than to "bestärkt" and I think, once someone is convinced, they are convinced :-). So - maybe we should write: "... it may have given her another reason to think that she's right."
(One more thought "for the road" as it were ...)
What I would like to add is: in your first translation, you have used ONLY. This would be right, if the sentence contained NUR NOCH. However, we've got EHER NOCH which means something like "rather".