For someone who doesn't know what to spend money on, she's surprisingly set on the money. I don't want to call it greed, but taking over a noble's house for the wealth does sound like a villain's motivation.
The more important part, however, is that the idea of the marriage being for reals has been broached. If the idiot didn't mention it, she never would've realized, so this is really his own fault.
Since she made an oath, she should probably leave it alone? This doesn't seem to be a problem anyway, considering how attached to Julius he is. She'll find out the truth when she finds out.