FRIDGES:

Basically, the current CR survey results (of 61,000 CR members with newer fridges) show Whilrpool models to be the most reliable.

Maytag and kitchenaid are brands used by Whirlpool, not Frigidaire (which is actually an Electrolux subisidiary).

Whirlpool also makes some of the refrigerators that Sears sells under its Kenmore brand. The other primary Whirlpool Corp. brands for fridges are Whirlpool, Whirlpool Gold and Amana. Whirlpool bought Maytag/Amana after bad management nearly wrecked them over the last decade. (On the other hand, I've still got my vintage 1998 Maytag 2156. It met the 2001 Energy Star requirements and is barely less efficient than those meeting the current standards.) By the mid-2000s, Maytag and Amana had a deservedly terrible reputation for a while, enough so that it continues to poison the results of the Consumer Reports reliability surveys which go back 6 or seven years. Check out the link below for a recent extensive discussion of these brands in the context of bottom freezer fridges

Kitchenaid fridges are gussied up versions of the same thing that Whirlpool sells under its other brand names. Kitchenaid comes back with slightly less reliability basically because almost all of them come with ice-makers and a high proportion of them have through-the-door ice-makers and water dispensers. Ice-makers and water dispensers are the components that can be troublesome and account for a goodly proportion of defect complaints. This is true of all makers.

Again, check out the link below because it will lead you to other resources.

DISHWASHER:
Tons of threads on these including low and high end. For basic dishwashers, I am partial to the basic Ascenta Bosch models. Look for sales on Columbus Day. It has a combination stainless and polypro tub and gets pretty high marks from CR. What I like is that they run relatively quickly. A lot of the Whirlpool and Frigidaire that I looked at recently had very long cycle times (like more than two hours). Do you have access to CR ratings?
Getting stainless steel exteriors usually adds a hundred bucks to the price, but holiday sales can help lower that cost a bit. (Pretty much true for all appliances, btw.)
STOVES:
Gas? Electric smoothtop? Coil burners? Induction is nice but may be pushing the budget. The least expensive one I've seen recently was Samsung's new NE695 freestanding stainless induction stove which was down to about $1250 at Best Buy over labor day weekend. IF the budget can accomodate that, then the next question is whether or not s your sister have much cookware already? Costco sells several sets of induction capable cookware for about $200.

MICROWAVES:
Hard to give specific advice without knowing more about the kitchen but there are tons of postings here about microwaves. Any space constraints? Does it need to go on a shelf? Will it sit on a counter or cart? Are you looking for an OTR? You can really save a lot of money if you do not need an OTR. Better to get a inexpensive externally venting range hood and an inexpensive microwave.

EXTENDED WARRANTIES are only as good as the service companies to whom service is outsourced. Several of the national service companies have awful reputations. For a sense of how good or poor warranty service. Check out consumeraffairs.com to see what warranty service can do to a manufacturer's reputation.

Here is a link that might be useful: Need a new refrigerator, any recommendations on which one?