Average A time for that age is anything from 3-4 hours, so it is possible that her A is short for her throughout the day and she could do longer A earlier and get better naps throughout the day. If it were me, I would try upping her first A and try to get the longer nap earlier in the day. Increase by 15 mins and hold it there for 3 days, then if need be, increase again and see what happens.
As she's 8 mos, I would suspect that a 1.5 hours nap that late in the day will set you up for trouble at BT, that's just a hunch of mine! Do let us know what happened with BT today.