Bottle nipples

How do you know when to switch to faster ones? Dd is normally breast fed but is starting daycare so im giving her bottles too. She seems to take the playtex ventaire the best but last night my mom watched her and said she thought the nipple flow was too slow. Should I switch to the medium or fast? Is there a way to tell when its time to increase the flow? (my mom thought there was something about having bubbles or the size of the bubbles while eating)? I'm clueless

Dd is 11 weeks old
Ventaire has slow 0-3 which is what she's using now, medium that says 3-6 months and fast says 3+ months

Bottle nipples

I switched ds when he was consistently falling asleep during bottles and playing more then eating. He was 4-5 months before I went to level 2 inn Dr Brown's.

DD2 is 3.5 months and still drinks level 1 Dr Brown's nipples and slow flow from ventaire (she has them once or twice a day if I'm behind inn washing bottles! )