The witch said "You will not fall in love with anyone and no one will fall in love with you" as part of the curse.
With witches curses in stories and myths wording has always mattered hugely. I am pretty sure that if he and Alice kissed it would break the curse as it would disprove its claim of "never be loved or love" hence nullifying its effects. This is usually how their curses were broken, by word lawyering.
Even without her mother likely being the one responsible, i doubt Alice is immune, just that once they kiss, the curse is likely gonna be broken due to how it was worded.