If it is the opposite hun, in that the nights are worse after those great naps, then I'm thinking she's getting too much day sleep and that's robbing her night sleep.
2x 2.5hr naps is a lot of day sleep, I think it would be unrealistic to expect 12hrs NS after that. Perhaps you could look at capping the naps to 2hrs each? That really might throw your day off though. Do you think she'd be able to look at an increase in A time very, very slowly? So adding 5mins every 3 days or so?