Mis-aligned dish, obstruction, or bad cable or component.
If mis-aligned, she might get a signal in perfect weather, but have it fade in anything less;
Obstruction could come from trees, clouds with heavy moisture content, heavy rain or snow falling, leaf, snow or ice accumulation on the dish, or something blocking the LNB (the white plastic part on the arm that sits in front of the dish).
Cables, cable connectors, multiplexers, and/or the receiver itself could also introduce issues. These are usually (but not always) all-or-nothing problems, where either it’ll work or it won’t.
Tell her to call to cancel her service, saying she’s going to go to Dish, or to the local cable provider. They’ll do whatever it takes to retain her as a customer - usually including providing new equipment, and installing that equipment for free, AND reducing her monthly bill.
Unless she is getting Sunday ticket or maybe special language/international programming, I'd think Dish would be cheaper.
Might be worthwhile to call Dish and find out what they charge for a comparable package.