One thing I learned is similar to Patricia's statement: to get their attention, I connect, then direct.
For example, she's playing... acknowledge what she's doing. "Oh, look at this, you've got your baby doll all wrapped up (whatever she's doing)". Then, when you have her attention, give her a head's up: "In a couple minutes, we need to put your toys away and it'll be time for a nap." Then, stick around,play for a minute, and help her transition from what she's doing. "Will you get the dollies/toys ready for their naps?" (we did this at preschool/toddler group... 'putting the toys to bed' and you can actually cover them with a cloth) If she doesn't help, go on doing what needs to be done, then take her by the hand and get her ready for her nap.
At this age, she needs you to be authoritative and lead the way. Even when she doesn't want to do it, she needs it to be a 'fact of life', so be sure you are using authoritative language, as in "It is time for" instead of "are you ready/do you want to?" Be sure to own your direction instead of making it a 'friendly question' to which you will likely get a no response. Tell, don't ask.
She can have a few 'how' choices within this framework, which means that you can ask her "do you want to place the babies over here, or on a pillow for naptime?" or 'will up pick up the blocks or the kitchen toys?' -- it's getting done, but she can choose *how* she does it. Don't bombard her with them, of course, but do give her a little room to have some control over a task she needs to do. "Do you want to pick out books first or go potty/diaper change first?" These are friendly ways to engage her through an unwelcome transition.
And if you feel she's growing out of the nap, then do offer to let her play quietly with a few soft toys on her bed or look at books. Kids this age aren't great at taking quiet playtime on their own for too long, so don't expect her to stay in her room/on the bed for more than 5 minutes to start. (if she's still in a crib, you might have more success.) Do set a timer for ten minutes and then come back and check on her. I've found that when I start kids on 'quiet time',(and usually at a later age) most of them need me to keep it short. Always use a timer, so they know that quiet time *will* end; they will grow more comfortable with playing on their own if they trust that they'll have that ending. And then, add on a little more time each day, even if it's just two minutes at a time. But don't expect too much, too soon.
Good luck!