JUST FOR QUICK REFERENCE:
Save the game often and use all your save slots.
Keep saving over your oldest one if you are satisfied with the way things are going in your game. If your not go back to one of the others and try again.
You can also load last checkpoint. theres usually one everytime you go into a new area.
Use Y it calls your survivors to follow you. When you use Left Trigger then Y you can tell your survivors where to go and they will stay there as long as you don't press Y again.
Grab the leadership book in Rags Mags it helps alot.
Give her a good weapon
I found it better to stay ahead of her and let her catch up because when she is moving the zombies don't mess with her as much. Just watch the little picture of her that shows up if she gets into trouble.
Heal her often(after safe room visits, attacked by too many zombies, or psychos, or you by accident)
Be carefull when she is surrounded if you do to much damage to her she will defect and you will have failed.
Leave her behind every time you go to the safe room.
Try to be quick in the safe room so you dont do to much damage to Denyce.
During the case where T.K.s robbing casinos put her in the bathroom or maintenence room and save it if you can.
When the snipers show up stay away from the Strips, use the short cut.
There will be a case to stop T.K.s helicopter, make sure that you leave Denyce in the Royal Flush Plaza somewhere safe. Do not bring her with you because you fast travel to the safe room when the fight is done and she goes with you. You will need do this part quick so she does'nt die.
Once the army shows up and fails you can go straight to fight Sgt Boykin if you want and think your prepared. Just get her to attack him once and the cheeve is yours.
MORE IN DEPTH STRATEGIES:
First thing you want to do is go to the bookstore (Rags Mags) on the second floor of the Royal Flush Plaza. Grab the leadership book, its in the entrance of the store to the left on the ground. This book will make the survivors more effective while in your party making them smarter and the crippled ones can run on there own. While your on the second floor near the book store there will be an advertisement sign you can climb on and there will be a broad sword.
Next get Denyce from Roy's Mart during the case to get the Zombrex. I don't remember the name of it but it's the first thing you do once your in the plaza. Give her the broad sword or any strong basic weapon (sledgehammer worked pretty good for me too) so she can defend herself well.
Now from here you can choose to do only the main story cases if you dont want to deal with other survivors making it more difficult, (but that way is kind of boring to me) or play through normally trying to do as much of the side missions as you can.You may want to do the Wilted Flower case to open the shortcut, it will make it easier when the sniper guys show up to not even go out to the Silver Strip, Platinum Strip, or Fortune Park. The snipers do alot of damage and can take survivors down in a few shots.
If you need to go back to the safe house for any reason always make sure you leave Denyce either in the maintenence room or the room across from it in the hall to the vent leading to the safe house. If you have survivors with you then you will need to try and seperate Denyce from them so she is alone in one of those rooms. Use the left Trigger and Y to seperaet them into different rooms to get Denyce alone then leave her there in a room.
After safe room visits she will have taken damage depending on how long you were there. There will always be 3 creamers in The Dark Bean right out side the hall leading to the vent. They should heal her quite a bit but if you need more there's an orange juice in Yesterday, Today, and Tomorrow which is nearby.
When your fighting bosses leave her in a maintenence room or other room where she will be safe. Most of the time she wont spawn right next to you after the cut scene. When i fought the clown on stilts she did spawn next to me so be carefull if she does put her in a room quickly.
There will be a case to stop T.K.s helicopter, make sure that you leave Denyce in the Royal Flush Plaza somewhere safe. Do not bring her with you because you fast travel to the safe room when the fight is done and she goes with you. You will need do this part quick so she does'nt die. Roll a lot, time them so you roll under the crane arm then press B on the winch and throw the guard rails at the helicopter they do alot of damage.
Once the army shows up and fails you can go straight to fight Sgt Boykin if you want and think your prepared. She only needs to damage him once then it will pop. You might want to try it with a gun but for me she hit him with a sledge hammer while he was shooting me on the ground.