Jenifer, she will give you signs when she is ready. If she is doing well on 2 naps then let it be for now. Mine transitioned finally at 15/16 months but I started cutting her morning nap at 12+ months. Cut it to 45mins and then towards the end of the transiiton down to 30mins.... eventualy she would play instead of sleep in the morning and that was my cue to go to 1 nap.
Some do it as late as 18months so not all babies are the same. Some of the signs are early wake ups, fighting the pm nap or the pm nap being pushed too late, taking a long morning nap and a short pm nap....
I can understand you being afraid of waking from the morning nap and the pm nap not improving, but its worked for ALOT of us here (me personally with Isabella and now doing the same with Jasmine). If you are finding that she is fighting her pm nap more and more then cut the morning nap ato 1hr to start, bring the 2nd nap forward and see how that goes.....
hth
Layla