Essentially 100% of first pass students will simply use letters from their podiatry faculty. If you participate in research you might ask said professor for a letter.
Now for the burn.
No matter how well you know a professor it is entirely possible they will write a garbage template form letter. The letters are of such poor quality that they really contribute nothing and honestly barely warrant a glance except to make sure they don't say something bad.
Last of all, a pre-podiatry letter really can't be worth anything. The person observed you as a student - not as a podiatry student. So they can't have really held you up to any standard other than a person who shadowed.
Perhaps your situation is different but I would simply tell you - this isn't worth fretting about. Don't maintain contact for the purpose of a letter. Maintain contact because you are going back to the area and want to be their peer, want a future mentor, genuinely like the etc.
And because I can't help myself - and when the time comes this person who opened the doors of podiatry to you will offer you an associate salary of $75K / 30% collections
wink wink!
Just for your amusement - people who don't match the first time usually show up with a diversity of letters ranging from local pods they "preceptored" with to faculty writing letters explaining their weaknesses and what they did to correct them.