Is it ok to let my 3 month old breastfed baby sleep until she wakes up to feed? or should i wake her to feed her?

It's OK: Let her sleep, but remember, she'll be that much hungrier when she wakes!

Depends: This depends on how you want to live. I favor mom's getting good sleep. That means never letting them sleep more than 2-2.5 hours in a single stretch during the day, and letting them sleep as long as they want at night. Otherwise a long day nap flips their day/night cycle.Have them wake up eating, and settling to sleep alone without refeeding.Works well.