General objectives: You shouldn't go after Heather if you didn't eliminate Jennifer, because otherwise you would have to return to the start area. Heather McCarthy can be found on the motel's parking lot when you start the mission, however later she travels to a local amusement park and that's where you should attack her.
An interesting thing to know about Heather McCarthy is that the game allows you to murder her at the very beginning of the mission, because that's when she'll be briefing her men at the parking lot (screen above). I strongly advise NOT to pursue this course of action, because shooting her will alarm all Agency soldiers and you would be forced to fight them in an open combat scenario.
I recommend that you acquire Agency's soldier disguise from one of the attacked enemies before heading to the next area. Once you have the disguise go to the opposite end of the motel's upper balconies. Your goal is to reach a staircase leading to the ground floor (screen above).
Start using small brick walls for cover and make sure you're doing that even before reaching the ground floor so you won't be noticed. I recommend that you use the opportunity that enemy soldiers are taking part in a briefing and quickly explore nearby motel corridors. Move between covers, searching for interactive objects along the way. The most important object in my opinion is the rat poison found in one of the corners (screen above). You can't use this item right away, however it will come in handy later on when you'll start thinking about possible ways of eliminating Heather McCarthy.
The rat poison mentioned above isn't the only important thing you can uncover here. New evidence is in the area and you can find this collectible in the middle on the parking lot, on some crates near parked cars (screen above). The best way to safely obtain this item is to use instinct to hide Hitman's true identity, however you can also use throwable objects or activate car alarms in nearby cars to distract Agency's soldiers.
Your next task is to safely get to the other side of the parking lot and obviously it's not easy, because the area is swarming with Agency soldiers. There are two ways of reaching your goal. The first possibility is to circle the middle of the parking lot from the left side, using nearby vehicles for cover (screen above) and moving between them when it's safe.
If you've decided to hide behind cars, then eventually you'll get to a much bigger bus (screen above). You shouldn't encounter anyone here if you're playing on lower difficulty settings, however if you've chosen one of the pro difficulty levels then you'll most likely find a single guard here. Eliminate this guard or avoid him while trying to stay away from his line of sight. Inspect this area if you have the chance, because you can find remote explosives here.
In order to leave the parking lot safely you must avoid one more Agency soldier and he can be seen on the screen above. The best way to do that is to move as close to the left fence as possible so that he won't notice Hitman sneaking behind his back.
The second method of getting to the other end of the parking lot is to circle it from the right side (screen above). In this case you should make your move before the briefing is over.
Use instinct if necessary, heading towards a small passageway displayed on the screen above. It doesn't matter what difficulty level you're playing on, because this exit from the parking lot shouldn't be guarded by anyone.
Both paths described earlier in the text will allow you to reach a small minigolf course with an Agency soldier and an innocent civilian. You can act in two different ways here - save the civilian or wait until he's murdered before making a move to eliminate or avoid the guard. If you plan on killing the Agency soldier, then I recommend strangling him (preferably with a fiber wire).