Looking strictly at specs can lead you astray in laptops, and unlike desktops, it is difficult to fix problems by replacing parts. Like others have mentioned you need to check the laptops out in person or, at the very least, read some reviews on the laptops you're interested in.
With your budget, you shouldn't try to investigate every possible option - the ratio of garbage to good is way too high. Start by going to some review sites and just picking the laptops with the best reviews and find the ones in your budget range with the specs you want. This should significantly narrow down the ones you need to research. Make sure you read the reviews though - you'll pick up on stuff that just looking at the typical specs won't tell you. Such as if the laptop has a crappy track pad (this is actually a fairly common problem). Is the battery run time short? You definitely can't trust the manufacturers on that spec. Does the keyboard feel good to type on? Does the monitor have good viewing angles? Does the monitor produce the proper colors? Does the laptop get hot? Is the SSD actually fast?
Macbook pros are one of the good options that would fit your constraints, although there are others( I hear that certain Lenovo and Sony models are quite good). Keep in mind that you can get refurbished macs that come with the same warranty as brand new macs at reduced prices from the apple website. You can also find new macs at reduced prices at various online sites. For example, Macmall.com is a reputable site that typically has good prices. You should also know that it is widely expected that Apple will be introducing at least one or more of the new macbook pros in June (expected at WWDC). They are rumored to have retina displays - even if you don't care about having the latest and greatest, if you can wait, you'll be able pick up the old models (the ones that are current at this moment) at reduced prices.
It would also be a good idea to remind your sister to be gentle with her laptop. It seems obvious, but I've seen people just drop their laptops onto desks or drop/toss the bag containing the laptop.