Your daughter is thae same age as mine, and even tho she may not quite have teeth yet, their gums are quite hard at this stage.
I have Melissa on Kumera, ( I don't know if you have it over there!! - it's NZ potato) which is a little sweeter that plain potato, but she is a good eater at the mo, touch wood.
But also have you tried sweet potatoes? They could help. Also, do you give her canned baby food, or make your own? The canned stuff can quite often have access sugar (that they never tell us about!) and maybe puree your own apples and pears or something? i know it can be tedious, but I hope it might help. Even you own custard.
Rhubarb can be quite bitter/sweet too.
If I think of anything else I will post another reply!! smile