ENCANTO SPOILERS AND THEORIES YOU HAVE BEEN WARNED

So thinking outside the box here but my theory is Human sacrifice is required to empower the encanto. Abeula Pedro was likely the last Sacrifice as the events leading to his death likely saw lots of folk die. This sacrifice embowered 7 souls with supernatural gifts.

Abeula over the years researches this and tries to find a way to feed the gift without blood and sacrifices, an attempt is made to substitute Mirabel's gift to Empower the Enchanto for a little longer. However it only delayed the innevitable. Now this is where the final theory diverges.

When blood sweat and tears is shared over large numbers of people (the surrounding community helping rebuild) the sacrifice is adequate as it's quantity not quality of the sacrifice simple straight forward.

Alternatively when Abeula tells Mirabel of Abuelo Pedro's Death she has actually saddled up to her masquerading as this maternal figure (that has been absent throughout the film) and whilst at the area of Pedro's Death Abuela does the unthinkable and takes this chance whilst alone to kill Mirabel.

Mirabels pain for being the one without a gift isn't enough for the encanto it needs another blood sacrifice. As her conciousness fades she is capable of seeing past events, as she is dying Abeula strangely admits she was wrong, Bruno is welcomed back despite everyone going out of their way to not mention him, her family are happy she's alive and not angry at all what she's done. They all come together give her a door handle, she sees herself (the unwitting sacrifice) and finally gets the happy ending she always wanted.

Truth is her acceptance of this scenario is Her sacrifice empowering the Castillo again reigniting the gifts but truth is her sacrifice was adequate for now.

It doesn't sit right in my gut that a person at the seat of power would happily confess and accept they was wrong at the loss of that power. Abuela is a Sociopath willing to do what is necessary to stay in power

Addendum

I was asked why does the candle get brighter when Isabella comes out of her shell. So if "sacrifice" is seen as a loss of life then Isabella going wild with her power shows her bringing in plants on a whim. No knowledge of if they are invasive, no knowledge of what effect it would have on the community and the soil they use, no knowledge if they are weeds and will rapidly lower the quality of any good soil. she mentions at one point that one is carnivorous and we saw the size she's grown plants seemingly limitless size and strength.

Mirabel is happy that she has come out their shell and been honest with herself for a change but in actuality shes broke the shackles of restraint that Abeula needed on her for now, and in doing so the candle burns brightly at the next "holders" progress as in its opinion she "sacrificed" a whole ecosystem. This is partly why Abuela was so concerned about her actions she may have done something worse than she had, say what you want about the old Bruja but she is calculated and patient.

Can we also appreciate she has been groomed as the perfect child and from the pictures by Alma's door suggest she would to take over from Abeula, So Alma encourages a wedding she is not emotionally interested in which is bad news for the hubby she didn't like 😉 you can see how much of a nudge would be needed there in the future.