Are you looking to DIY? If so, if you've got some basic DIY skills and you can get your head around some alarm terminology and programming, then if you want a fob based system, the Texecom Premier 24 is a pro panel that's easily available, decently priced and will replace the Accenta 6 without too much fuss.
One thing I will warn you of though is that a more advanced panel like the Premier comes with its own problems in regards to something called "alerts". All professional panels have to notify the user of any faults ie power cuts, battery faults etc. These can be a pain to reset for some users, so if your wife finds the Accenta hard to use then she may struggle to clear any alerts and set the system. The Accenta is one of the simpler systems on the market when it comes to full setting and unsetting. The part sets require a couple more button presses, but it's not what I'd call a difficult panel to use.
If you do go for a Premier (or any other panel), don't forget to include a SLA back up battery (my recommendation is a Yuasa NP7-12 if you go for the prem) and check it comes with the prox keypad. Whilst you're looking, the Accenta 6 is a pretty old system now, which may also mean old sensors and an old bell box. May be worth spending a few extra quid and swapping all the bits on the ends of the wires while you're at it. It'd be a shame to spend the effort changing the panel and getting rogue false alarms because the original installer used some cheapo PIRs!