M4tt makes a lot of good points.
Ten years ago when we (Mrs Captain and me, not M4tt and me
) were looking for a weekend retreat property we wanted something on the coast 2hrs max from London, we'd spend many weekend traveling the coast looking for likely spots, starting on the Norfolk coast and ending up in Bournemouth.
When we found a area we liked we'd go back and stay a weekend to try and get the feel, if that worked we tried a week if posable, in reality there were only two areas that got the weeks treatment.
We ended up in a small village between Worthing and Littlehampton so the same stretch of Sussex coast as Brighton.
Apologies for the long run in but if you friend is looking for an 'escape' from London Brighton might not be the place, the congestion, pace and bustle there might be too close to London to make much difference. (Our experience, for us it didn't even warrant a weekend trial)
There are many places on the same stretch of coast that have good access links into Brighton for a 'fix' of urban living without being in the thick of it all the time.
Perhaps take a look at Shorham-on-sea or Worthing as options, if nothing more it might confirm Brighton is really the place she wants to be?
Either way I recommend trying to Air B&B as close to any desired areas to get a feel for staying there on a full time basis