The mixture of antidepressants and alcohol causing a blackout alone is not realistic. Maybe just have her drink a lot of alcohol? More realistically (albeit darker), you could do something similar to what the hangover movie did. Maybe even have a drink switch up where the woman intended to be drugged is not (and this ends up alright) and the girl in question is taken home by her friends because she’s acting super drunk.

Different effects depending on the antidepressant. https://www.drugs.com/article/antidepressant-medications-alcohol.html

Avoiding alcohol is a good idea, especially when taking any type of medication.

There’s a very wide range of things that could happen when you mix anti-depressants and alcohol. The drug, the dose, the amount of alcohol, the person, what else they did that day, and about 100 other factors would all be relevant in the likelihood of that happening.

Is that outcome possible? definitely.

Realistic is more of a subjective bar. But people get blackout drunk all the time without antidepressants, I would think most readers would treat it as realistic. Particularly if you have her drinks a lot of alcohol, and wake up with symptoms of a hangover.

https://www.drugs.com/food-interactions/brexanolone.html

Brexanolone and Alcohol/Food Interactions

There is 1 alcohol/food/lifestyle interaction with brexanolone. Moderate Alcohol (Ethanol) brexanolone

Moderate Drug Interaction

Using brexanolone together with ethanol may increase side effects such as dizziness, drowsiness, confusion, and difficulty concentrating. Some people may also experience impairment in thinking, judgment, and motor coordination. You should avoid or limit the use of alcohol while being treated with brexanolone. Do not use more than the recommended dose of brexanolone, and avoid driving, operating machinery, or engaging in potentially hazardous activities requiring mental alertness and motor coordination until you know how the medication affects you. Talk to your doctor if you have any questions or concerns. It is important to tell your doctor about all other medications you use, including vitamins and herbs. Do not stop using any medications without first talking to your doctor.

https://www.drugs.com/mtm/brexanolone.html

What is brexanolone?

Brexanolone is used to treat postpartum depression.

Brexanolone is available only under a special program because it can cause excessive drowsiness or sudden loss of consciousness. You must be registered in the program and understand the risks and benefits of brexanolone.

Brexanolone may also be used for purposes not listed in this medication guide.

Alprazolam is a benzodiazepine used to treat anxiety disorders, and it causes exactly what you’re talking about if you take it with alcohol. It’s not an antidepressant but it’s sometimes used for people with depression, at least at first.