My DS1 (ASD) has always pointed, indicative and proto declarative - it's just that the range and the purpose is limited to interests/obsessions. I think there is a lot of misinformation about this pointing issue. But yes acheiving the milestone late may in itself indicate ASD.
Yes DS 4 , asd, now points at a lot of things such as constant pointing of cars and motorbikes with a 'look... motorbike, mummy!'. However, at age 18 months or so he didn't point , by age 2 still no spontanous pointing, we 'taught him' how to point. But his pointing isn't always clear, i mean he often uses his whole hand or curl his fingers while pointing. Again pointing in asd kids can varie, but usually it seems pointing is delayed.
That's terrific that your DD has started to point with an index finger. I didn't notice DS2 much at the relevant ages but remember a hand-gesture point at around 2, then index finger pointing around 3 like your DD.
At 4, we've truly cracked it as he's now doing the point-and-look-behind-you-to-see-if-mummy-can-see-it-too thing and you know what? He does it just as well, and conveys just as much information, and learns as much, as all the other 4-year-olds who've been doing it from 18 months. It's a foundational skill, and that little bit of the foundations is now complete and the building is that bit steadier. It makes me really happy to see it - an endless source of pleasure.