I used to teach preschool before becoming a SAHM when my younger son turned 3. Here is what worked for me:
I agree that consistancy is the key. If you do not have enough time for rest time on the weekends, make it shorter. But, by all means, have one (even if it is only 20 or 30 minutes).
When you put her down for the rest time, set a timer. Tell her you are setting it; let her watch you set it. Put it where she can hear it, but put it outside of her room. Tell her that when she hears the timer she can get up. If you feel she needs more time on any given day for any reason (even if YOU just need more time), you can reset the timer because it is out of her sight.
I used a timer with both of my boys and even sometimes in the classroom. It is a WONDERFUL tool for kids to learn that things they do not WANT to do (but NEED to do) don't last forever. It can be used for a lot of things, too (time out, meal time, nap, taking turns, etc).
I hope it helps. :o)
Blessings,
P. <><