Mil will not put baby down for a nap!

So my mil watches my lo on Monday’s (which I’m grateful for) but she will not put her down for a nap! She’s 19 months old now and even knows how to go to sleep on her own. I usually just put her in her crib with a blanket and she’s fine...but my mil just lets her play and by the time I get there to pick her up she’s super fussy and just wants to go to bed for the rest of the night. It pisses me off because I’ve told her multiple times “her nap time is at 12:30” “just put her in the crib and let her cry for no more than 10 minutes, she will eventually fall asleep”. Now when I pick my lo up today I know she will be in shitty mood and will just want to go to sleep. Ugh....