Yes it does. But just the trip up to the sat is longer than any round-trip on earth, and then your request has to come back down, plus the reply also has to go up and back down, and all of that (500ms best case) gets added to whatever the remaining trip
through the fiber on the earth is.
Many web pages aren't just static content any more. What she's got from AT&T isn't "really low latency". I would call that "fair", while 500+ ms is just plain awful. Personally, I would rather have a low-latency connection with less bandwidth that a high bandwidth connection with a guaranteed 500+ ms of latency. No, I'm not a gamer, I just run my business remotely via a VPN and have seen first hand how much an increase in latency affects things, regardless how much bandwidth is available.
Anyway, since the bandwidth and data caps on her AT&T plan are comparable, but the latency is an order of magnitude lower, and the cost for the same monthly GB allotment is less than half, the AT&T plan is by far a better deal.