Slightly complicated by a lowish offer fromRH which is unconditional if she firms it
I always think this looks a bit desperate by the university - we're seeing a number of competitor places doing it.
They are both excellent places for an arts degree - she'll have a great time at either, and be challenged & stretched.
But they're very different universities, so it might come down to "feel". I love Egham, but when I taught at RHUL, I wasn't an 18 year old who was away from home for the 1st time. When I lived nearby, Egham was very quiet on the weekends. I think the more cautious students liked it because it was London-but-not-quite-London, IYSWIM.
And I adore Leeds, but is she used to big cities? Leeds is a fantastic student city, but it's a bigger city. The University is one of the best in the country - in my field it's really superb, and that field feeds in to the liberal arts offering. Excellent library too. I used it quite a lot for something I was writing a while back.
Either way, she'll have a great time & get an excellent degree.