Should I upgrade my car?

I have a 2000 Ford KA which is a great little car - has served me very well. The reason I'm asking is that my girlfriend is going to university 3 hours (around 120 or so miles) away. I'm not certain how well my KA will do (in terms of it being economical or reliable, especially on motorways!)

Do you think it will be ok on the motorways, or do you think I should sell it and buy something a little bit better for the motorways? If so, what would you recommend (was thinking a long the lines of a 10 year old car, an A3 or Focus or Golf etc. And what engine size? Bearing in mind insurance, have been driving for a year NCB and i'm 19 years old.)

Of course

Buy a new car for her. She deserved it.
Buy something she is comfortable driving in it. It still need to be safe and reliable.
A 2.5 liter 4 cylinders engine is all you need. It has enough power and will save you on gas.
Don't buy an older car. Remember you want to upgrade your car, not degrading it.
I like sport cars, but I wished I have a Subaru Forester to drive in the winter.

I'd save up and buy something that's only 4-6 years old, so there won't be a lot of mileage on it. Going for a 10 year old car isn't much of a step up, so don't bother with that.

If the Ka is running well and you keep it properly serviced a 120 mile journey is nothing to worry about.
The car is 14 years old so be sensible, sit it on 65mph which won't strain it in any way and it will get you there and back with no hassle and with good fuel consumption. People who have small and old cars often seem to be worried about motorways but what they probably don't realise is that their small car has an engine with as many or more bhp than large family cars of 40 years back had. Legally there's no where in the UK you can drive at more than 70mph, sure there are people flying along at 100mph but there are also people who put their heads in a gas oven. Stck to the speed limit, make sure your oil and cooling fluids are at the recommended levels and the Ka will give you plenty of economical motoring yet.