Breastfed babies are a totally different animal than bottle fed babies. I read on kellymom.com that from about 1 month old to around 6 months old breast fed babies actually eat about the same amount at each feeding! So it sounds like your little one is doing what she needs to do.
Both of mine still woke in the night to nurse at that age. Parenting doesn't stop at night no matter how tired we are. ;)
My daughter was a power nurser. She rarely nurse longer than 7-8 minutes at that age. She was in and out and done lol!
Neither of my breastfed babies ate enormous amounts when they were given a bottle of pumped milk. I always stare in awe at bottle fed babies and the volume they take in. Mine never ever took an 8 oz bottle. Maybe 5-6 max.
Please do not go by the charts that your doc is using. Most likely it is based on formula fed babies. Again, totally different animal.
It is best to delay solids until at least 6 months and then only when baby shows signs of readiness. The reason we are told to wait is because baby has an "open gut" meaning everything they eat passes into the blood stream. I had one start solids around 7 months and my second was over 9 months old. Solids are for practice, to a small degree to supplement the primary nutrition of breastmilk but not to replace breastmilk! Again, follow baby's lead.
Bottom line is nurse her on-demand, round the clock 24/7. You never, ever put off a breastfed baby! Just follow her lead! She is telling you exactly what she needs and when she needs it. Breastfed babies are amazingly adept and getting what they need.
Don't be surprised if she hits a grow spurt soon (around that 6 month mark) and is nursing even more for a week or so. That gets you to make more milk (and the amount she'll take in) for these next 6 months.