You play French version?Maybe there is a bug in that version...I have not experience this before,I play English version.
How about the other villagers that you have been talking+gifting everyday for one year?If you didnt miss any day talking and giving gift every single day,it wont be very hard to earn hearts..
For Antoinette,I suggest giving frogs,which is FREE and can be easily found during rainy days.When it rains,search everywhere,and catch as many frogs as possible.(or chocolate which is quite cheap.)
Then,everyday,talk to her(+100fp) and give a frog to her(+150fp ),you earn 250fp per day.
1 heart in library = 6552 FP.
6552 FP divide by 250FP=26.xxx days
Which mean at this rate,(theoritcally...),you will earn her first
in one month.
If just talk to her EVERYDAY,+100FP per day,you will still get her first heart in 65days(2-3 month).
If you take one year to do that,that means you ignored her before(didnt talk to her more than one week) or there is a bug...
I am in 2nd year summer and most villagers whom I talk and give gift often have at least 5 heart,some even full hearts.Antoinette has 8 hearts.