Because stepsiblings do not share genetic material and often meet later in life, the natural biological aversion to mating with siblings (known as the Westermarck effect) may not be present. It is entirely possible that she has developed a genuine crush and does not know how to handle it appropriately within the confines of a family structure. 4. Harmless Personality Traits

Yes, it is entirely possible to transition from an uncomfortable, flirtatious dynamic to a healthy, supportive sibling relationship. It just takes time, patience, and unwavering consistency.

Try: "That comment makes me uncomfortable. Please don't say things like that to me." Reinforce the Sibling Dynamic

In a traditional sibling dynamic, boundaries are established over a lifetime of shared growth. In a stepsister dynamic, those boundaries are suddenly forced upon both of you. Flirting can be an unconscious way of testing where the lines are drawn in this brand-new, unfamiliar relationship. 3. Misplaced Romantic Feelings

Deciding whether to involve your parents is one of the toughest parts of this dynamic. You don't want to be a "snitch" or cause a fight between the newlyweds, but you also shouldn't have to carry this burden alone. When to Speak Up You should involve your parents if: You have clearly asked her to stop, and she refuses. The behavior escalates to inappropriate physical touching.

When she crosses a line with a comment or physical closeness, do not laugh it off or play along. Use clear, non-negotiable language.