hi thank you for asking your concern madam and welcome to hcm. green stool after starting feed apart from breast milk is weaning stool which is completely normal. it is a bowel adaptation to new foods. if your baby is active alert gaining proper weight then no need to worry. please do not give any antibiotics for it because that will harm the normal gut flora of baby, so dont worry about it. rash at perineal area is seems to be diaper rash if you use diaper for her. if not it may be a irritation to stool. i would suggest you to use different diapers like airated or disposable, do not wear it tightly, try to avoid diaper for most of the time and keep area open, clean without soap and clean with warm water only, you can apply zink oxide cream for redness and pain, xylocain oinment can also be used for soothing effect. if you see any pustules or wound is not reliving with these efforts then please visit your doctor for rash. if you feel any doubt please ask us regards dr. abhijit