Can a girl get pregnant after having a transsexual surgery?

No. Sexual Reassignment Surgery, or SRS, always comes at the expense of losing the ability to have children. In a female to male individual, his vagina is reshaped into a penis. In a male to female, she has a vagina, but cannot be given a womb, hence, cannot become pregnant.

BTW, this is transsexual surgery, not "transgender" surgery, since the surgery corrects the sex and does not change anyone's gender (who they are and the nature they were born with). True-transsexuals are a subset of the Mainstream Community, not the TG nor LGBT community, unless of course they are LGBT after their surgery. Most TGs are not really the gender they seem to present enough to want or need the surgery. See, transsexuals are gender conformists and simply were born with the wrong body, while TGs are gender variant and have no real need to change their bodies. Transgender tends to mean someone is between the genders, while TSs seek to become full members of a single gender.