When your divorce is bifurcated, the court legally ends your marriage but some important issues remain open to litigation. This enables you to move on with your life while buying some time to reach a marital settlement agreement or prepare for trial. Bifurcation typically occurs when one or both spouses petition the court to allow it.
Unless you and your spouse reach a marital settlement agreement, bifurcating your divorce involves two separate hearings. The court legally dissolves your marriage at the first hearing, then a judge decides outstanding issues, such as division of property, debts, support or custody, during a trial. In the interim, your ex can raise new issues pertaining to anything that was reserved or held over for decision at the trial. However, this technically isn't "suing" you because there's already an open litigation. If your ex was the one who filed for divorce in the first place, she sued you at that time.
Whether a divorce is bifurcated or traditional, one spouse can always take the other back to court after a divorce is final by filing a post-judgment motion. Your ex might do this if you've broken the terms of your judgment, such as by not following through with property division or by violating support terms. She can also file a contempt action over these type of issues. If circumstances have changed since your divorce and your ex wants to modify the terms of your judgment, she can file a post-judgment motion for this as well. For example, your original custody arrangement may no longer work because an older child wants to live with his other parent. A modification order would be necessary to adapt the divorce judgment to the current circumstances and to address the impact on child support.
There's also the possibility that your ex might want to sue you for damages in civil court, not family court, either while your bifurcated divorce is pending or after your divorce is final. These are tort claims, alleging you're financially liable to her for damages because you hurt her in some way. This isn't possible in all states because of something called "interspousal tort immunity." This legal doctrine prohibits one spouse from suing the other, before or after divorce. If your divorce is bifurcated, these issues can be raised as part of the divorce trial. Otherwise, civil courts may not be willing to address issues of emotional liability and damages after a divorce court has already ended the marriage. Your ex might have more luck if she's suing you over something like personal injury or fraud because you deceived her into agreeing to a settlement.