I haven’t been on an Alaskan cruise so I can’t speak to that. I have been to Hawaii and Kenya and my thoughts are that the two aren’t even in the same league. Kenya is a life-changing experience and Hawaii is one big tourist trap.
However, that doesn’t mean Kenya is automatically the better choice given the parameters you’ve outlined. Bear with me here because this got way longer than I intended.
If you’re really looking to just relax for a week, then Kenya is not the trip for you. It’s too far to go and not enough time to be there. The link you posted, though, is longer than a week and has an itinerary of 4 nights in the Mara and 6 nights on the coast, which is enough time for a short but decent trip. Personally, I would want that kind of trip to be for as long as I could swing it, and while the “start with safari, end with beach” is a popular combo, yours is a bit too heavy on the beach vs. safari for my preference. But, it might be fine for you if you’re happy to just get a taste of safari and then spend most of the time relaxing on a beach. You’d probably get 6-7 game drives with that itinerary which isn’t bad. You should find out more details about what type of vehicles the camp uses and how many other people will be on the game drives with you. There’s a big difference between 2-6 people in an open-sided Land Rover vs. 24 people in an enclosed van, both in terms of comfort and viewing ability/picture taking. Also be aware that your camp is not actually located
in the Mara, but in a conservancy just outside it. That can actually be a plus in some ways because the wildlife is probably just as abundant and you might have more freedom to get out of the vehicle than you would abiding by the rules of the park, but you should verify where the camp will be doing their game drives, how often they’ll be entering the park (because you’re paying daily entry fees), will you be attempting to see river crossings, etc. August is a good time to go for the migration.
The safari portion of your trip will not be what I would describe as relaxing. We were waking up at sunrise, or earlier, for the first game drive of the day, which lasted a couple hours and was sometimes uncomfortably cold (in early September). We’d return to camp for lunch and a midday break, followed by the afternoon game drive. Finish with a sundowner, followed by dinner and some time in the evenings around the fire before bed. The days were long and we collapsed hard onto our pillows each night. That portion of your trip also won’t allow your 18 year old to go off on her own if that’s what you meant by “not needing too much from me.” You’ll be sharing a tent and together on game drives and will most likely be escorted by a camp employee anytime you need to move from one location to another within the camp. Because yes, the elephants and lions and buffalo are very real and very deadly and they do come walking through the camps. This is not Disney. The beach portion of the trip may be where you find the relaxation and freedom for your daughter to do her own thing, depending on what types of activities are involved there.
The food will be delicious and your only regret will be having to leave, but Kenya might be a trip you could do better given more time and a different itinerary depending on what your goals are. And while it’s not as complicated to plan and pack for as most people make it out to be, PPs are right that you will need to deal with a few extra pre-trip considerations like visas and vaccines and that might not be something you want to deal with while studying for the boards.
I was not overly impressed with Hawaii but if you’re looking to eat well and relax on a beach for a week while giving your daughter freedom to go off and do her own thing, it might be a better choice for this trip. I’m not sure where you’re located — I noticed your Kenya trip originated in Atlanta. Hawaii is expensive, crowded, and can involve a lot of travel time, especially if you’re coming from the east coast. You said you’re open to returning to Costa Rica and I agree that’s a good option, especially if you’ve already been once to see different parts of the country and would therefore be content to stay in one place for an AI experience this time. Personally, I think Belize would be a good pick for you.