18 months sleep habits!

kasey
I've never had an issue with my little one sleeping. Lately, when I put her to bed at night she cries her eyes out! She eventually falls asleep though. She also cries her eyes out at nap time! 
I haven't changed anything - she only takes one nap. I just recently started putting her down for nap at 12. She wakes up in the morning around 7:30-8. But she fights me every single time to take a nap. I just end up letting her cry. 
Is she getting too big for a nap? Anyone else suffering front this? It hit out of the blue one day and I don't know how to handle it!