S.H.
Have a daily routine for naps and pre-nap. Everyday.
Let her wind-down first before nap.
If overstimulated, some kids can't nap.
If over-tired, it can also make them unable to wind-down and nap and they have a harder time falling asleep and wake more.
Tell her "YOU" are going to "nap" too... then with her, make everything quiet and calm and dark. Tell her to "help" you... then you lie down. Even if in her room or on the living room floor. Let her put anything/blankets down to get comfy. Then you tell her "this is nap time... quiet time..." and then do so. Turn off everything.
That is what I have done with my kids before, and it worked. And that way I actually got rest, too.
At this age, the often have sleep/nap tweaks. Its a phase. Thus, keep to your routines. Because they still do need a nap.
And if possible, put the baby down for a nap at the SAME time. That is what I did with my kids too.... and it worked. And I still do that. My son naps everyday still. And my daughter, for her age, will still nap sometimes too. We do it all together. I tell them nap time is ALSO Mommy's rest time too...
Don't "reason" with her. Just tell her... and you lie down too. Telling her this is not play time.... "this is the quiet room."
My kids, know that certain rooms are "quiet rooms" and others are "play rooms." It helps them to 'know' what goes on... it is patterning them and cuing them... and through repetition.. they will learn.
All the best, just some ideas,
Susan