I just purchased a couple Samsung Series 8 55" LED TV's for my house 3 weeks ago, and I have to say I am very impressed with them. It is the best (or one of the best) HDTV's available. The series 8 LED's cost me about 4.5k, but you could find a series 6 LED for under $2,000.
IMO, I wasn't to impressed with the Series 6. I needed one lower end HDTV and went with a 55" Panasonic over the Series 6 although they were the same price. The Series 7 and 8 are on a different level tho.
In your sisters case, If I was to buy an HDTV for under $2K, I would put in another $200 and go for the new Vizio 55" LED. It costs $2,199 but is supposed to be amazing. I have yet to see it in person, but maybe one of the other members have seen it (Possibly at Costco) and give more info.
VIZIO VF551XVT 55" LCD TruLED | VIZIO
If it must be under $2,000, maybe a Vizio 55" LCD or Sony 52" LCD.