My 9 month old baby girl is breastfed but not feeding well on solids. any tips on best solid food that can be given to her and the quantity required?

Real foods: Some babies at this age are just not interested in purees; try very small pieces of soft, whole foods (banana, avocado, other fruits and veggies) to see if she's more interested in those. There's no quantity "required" at all - if the issue continues, consider having her checked for oral texture defensiveness by a speech/feeding specialist.

Offer finger foods: Offer her finger foods. At this age, some babies don't like to be fed- they want to do it themselves. Put a few different types of food in front of her (in very small amounts) and let her choose what she would like to eat. Frozen vegetables (just thawed out under hot water), dry cereal, crackers, small pieces of cheese, soft pieces of fruits and soft, small pieces of meat are good to try.