Newegg is very trustworthy, enough so that they are on Google's list of trusted sites, and Google offers free protection on your orders from them that you can opt in on. I ordered a case from them a couple weeks ago and when I did, a message from Google popped up offering me this, so even if Newegg scammed me or whatever, Google had my back.
If that doesn't do it for her, show her some of the negative reviews on random computer parts. A lot of the time when people post negative reviews saying "it broke after a week" or something, a newegg employee will reply and help them get the problem sorted, often by sending them a new part.