It's going to get bad around 18 or so hours since her last dose, and will start getting better somewhere between 72 and 96 hours. She'll feel 95% in a week. That's the duration.
Has she been through this before? If it's her first true heroin WD, then she'll probably experience a lot of anxiety, fear, panic and mental symptoms that a seasoned heroin user has kind of learned to deal with by now. But she will be scared if it's her first time and it will feel like it's never going to end and that her head is permanently messed up. She will have cravings, BAD cravings, and may even try and trick you so that she can go get some H. Just remember that she's going through something painful and if she acts angry, aggressive, mean or even downright deceptive, she's kind of in a "survival mode" and you shouldn't take it personally. Heroin WD is really painful and it's hard to keep composure while going through it.
To help her, prepare her small meals that are soft/liquid, but don't force them down her throat. Ice cream is also helpful. Try and keep her drinking water or things like Gatorade. Around the 48 hour mark, she'll probably start getting "the runs" and be embarrassed about it. Just let her keep going to the toilet every 15 minutes and don't draw too much attention to it. It's totally normal. She'll also alternate between being really hot and really cold. So encourage her to get under the covers or to take warm baths when she's cold, and to drink cold liquids and be in minimal clothing when she's warm. She will sweat a lot and her sweat will smell bad to her, so help her constantly change clothes and even her bedsheets.
Use the klonopin sparingly, but maybe at night to help her sleep (if the Trazadone does not work, which is a possibility given how hard it is to sleep in heroin WD). It can also be used if her anxiety peaks because of how scary the experience is. But benzos like klonopin are also very habit-forming, so don't let her get too comfortable taking them. Do not give her any amphetamine. Stimulants, even caffeine, during WD can make it feel way worse.
Loperamide, which is the ingredient in Immodium, is an opioid that does not cross the BBB (so it does not cause any euphoria or psychological addiction like heroin). In a crude sense, it's like an OTC tapering/maintenance drug. Giving her Immodium in higher doses than suggested for its typical use should help lessen the severity of her symptoms. An OTC painkiller will also help with the muscle aches that she will experience. Vitamins too.
72 hours of feeling horrible is not fun, and it's worse when you don't get much sleep. But anything to make those 72 hours go by as fast as possible should be used. Movies, TV miniseries, documentaries. Listen to music. Play a board game if she is capable. Keep assuring her that she won't die and that she will feel much better by the 4th day.
You're a good friend for doing this for her. It's typical to feel like a piece of shit while in WD for all of the bad stuff you did during your addiction. Having the unconditional support of a friend during this time can make a world of a difference as she treads through those first few days with a clear head.