O no! Milk suddenly not putting 15 month old to sleep

[Tertius]

ive been putting her in her for with a bottle of milk and she's been falling asleep on it. Fine and dandy. But suddenly she has started to drink her milk and still be awake after... Could she have outgrown it? Or need a later bedtime?

I got her up again tonight (it was bed at 7pm) but she was eye rubbing and crying at 7:30 so I had to do the dreaded cc - no more milk wanted and she would Not let me rock her.

She naps between 11 and 12:30, so I'd expect her to be tired by 7pm...

Now I've done the first nights horrible crying, I may as well see it through. Any advice on timings? Bedtime after that nap etc?

Am I missing something obvious?