My daughter is interested in a top LAC such as Amherst or Swarthmore. She’s got very strong test grades, scores, and expects to be a NMF. She would love to continue swimming in college - her times are not fast (i.e. 58 100 free) but she’s a fairly new swimmer and hopes to drop times substantially over the next year. She just loves the sport, being part of a team, and being fit - she gets antsy if she doesn’t swim. 
She does not expect to be recruited, but we’re so confused as to the criteria for joining/making the team. Are all athletes recruited? Or if her times are faster than some others on the team (per college swimming) could she be a walk-on? If so, would she wait until she’s accepted to contact coach?
She could contact the coaches now with this very question
Not all student athletes at Amherst/Swat are recruited. But chances to make a team as a walk on would vary by the sport.
She should talk to coaches. Some D3 schools allow pretty much everyone to practice and have varying policies about who swims at meets (home and away typically having different levels of selectivity) and is invited to winter training. Others are much more restrictive. This depends on the general level of interest and the availabilty of the pool and coaching staff.
Just make sure they have a team :). She could maybe look at current athletes’ times and see where she’s more likely to be a “match” as a walkon or not. Being allowed to participate in practices whether on the team or not would be very cool.
You might also want to see if any colleges have club swim teams. Generally, those are pretty open to anyone who wants to join - tend to be on the same level as HS varsity.
@CCtoAlaska , the schools that allow swimmers to practice will almost certainly let them swim at certain meets (extra relays, extra heats) and they are in fact part of the team. Will they get a seat on the bus to an away meet, perhaps not. I know of one swimmer in this situation now, and she is not as fast as the OP’s D.
But it will depend on the school. Most schools recruit faster swimmers each year, so current seniors, former recruits, may be as " irrelevant" as the walk-on in terms of top in their event, but if the culture of the team supports them - focus on improving and PB -, it may be equally welcoming to a frosh walk-on. And yeah, there are others where you just get cut.
As everyone notes, your daughter should reach out with her interest to the coach. This is not for the purpose of getting an extra boost with admissions because, as you suggest, your daughter is not being recruited. However, it may inform your daughter’s choice of school.
It looks like both Swarthmore and Amherst have pretty good programs. But reaching out to the coach certainly can’t hurt and could help. Ask whether tryouts are open and what times are expected to make the team. Ask how many openings are predicted for the year in your daughter’s stroke. Some team needs (e.g., resulting from injury) may not be predictable, but sometimes coaches know that a prior year’s swimmer is throwing in the towel. If you have tapes, you may want to send them along.
You will want to look into the school’s policies about captain’s (out of season) practices. Many colleges do not restrict captain’s practices to athletes with a roster spot or, put differently, they must be open to all matriculating students. These will be critical to the non-recruited athlete. Captains regularly communicate with coaches about athletes at the margins who might not be stars, but could contribute to the team due to a work ethic, etc. Plus, coaches just have a way of knowing what happens in the off-season.
Let us know what the coaches say.
@gardenstategal thanks for explaining that. I am going to keep that in my head for the young swimmers I know who don’t get recruited but still want to swim.
Great questions that I hadn’t even thought about asking! So much to learn…
Club team is def an option if she attends a large Florida school - or some of the top 20/Ivy schools. (I was amazed at how fast some of the non-D 1 times are…!