Sounds like my just-turned two-year-old! Over the last couple of months she decided to start sleeping in a bed, cut two molars (two more to come), and got a cold. Getting her to nap on the weekends has been a big battle, despite the fact that she is clearly tired and she naps all week in preschool. They definitely hate to miss out on weekend fun by napping!
Can't say I've solved it completely, but some things that have helped are: black out shades, making sure that nap starts early enough, and being extremely firm about making her stay in bed.
I wait outside her door and halt any attempts to get out of bed or her room. If she makes more than a couple of attempts, then I tell her if she gets up one more time then I will have to close her door all the way (which she hates). She usually test me on this, I have to close the door, she cries, etc. But that's the last time to get up and sleep usually follows quickly.
I hate the crying and being "mean", but I've found with her personality (which 180-degrees different from her older sister), this is the only thing that works for her. Each kid is different -- good luck finding your solution!