Can my step mom who got her US citizenship petition me even if she is?
Maybe yes and maybe no. The USCIS Policy Manual section on family-based immigrants is in the process of incorporating information from the Adjudicators Field Manual (AFM). For now it has a PDF dump of AFM chapter 21. In AFM chapter 21.4(d)(2)(B), Termination of Stepparent-Stepchild Relationship (on page 104 of the PDF), it says: Normally, a step relationship terminates when a marriage ends, especially if it ends in divorce. See Matter of Simicevic , 10 I. & N. Dec. 363 (BIA 1963). However, under certain circumstances a step relationship may continue after the death of the natural parent or even after the legal separation or divorce of the stepparent and natural parent if there is an ongoing relationship between the stepparent and stepchild (see Matter of Pagnerre , 13 I. & N. Dec. 173 (BIA 1971), Matter of Mowrer , 17 I. & N. Dec. 613 (BIA 1981), and Matter of Mourillon , 18 I. & N. Dec. 122 (BIA 1981)). If the marriage ends in annulment, however, the step relationship is deemed to have never existed because legally the marriage never existed. So basically, if you can show that you have an ongoing relationship with your stepmother, she may be able to petition you despite the divorce with your father. Keep in mind that she can only petition you if she married your father before you turned 18.