Is she quite an alert baby?
Both of mine were (are) and yes, even at 8 weeks, too much to see before (or during) a nap would stop them nodding off (or resettling if they woke). Can you try darkening the room at all during the day (we use the Gro blackout blind which you just stick onto your window with suction pads) or perhaps try naps somewhere else darker/with less to see, and see if that helps?
As PP said though, it could also be a routine issue. What A time is your LO doing? Perhaps she is a bit UT and an increase could help.