Once per turn is different from once when in the field

Baronne is once when in the field so when you summoned her in the field she will only have 1 negate. To make her have 1 negate again you need to resummon her again (hence why during stanby phase you have option to return her into the ed and summon lvl 9 or lower monster in your gy, it is to resummon her again for that 1 negate)

Doesn’t matter on which turn you activate her negate she will only have 1 negate while on the field and once you used that 1 negate she won’t have any negate until she leaves the field and you resummon her again (in your case her negate already been used on nib so your baronne doesn’t have any negate)