I forwarded your question to a friend of mine who I knew could help you. She is involved with Special Education in the Lewisville ISD. Here's her response:
I know of several options. The place we take our son to is the Coppell YMCA. They have “adaptive swim lessons” that are 1-on-1 instruction, and the cost is only $50/month for weekly 30 minute lessons. That’s less than what I’ve paid for group lessons, so quite a steal! He has been going for about a year now and he’s made good progress. We’ve switched instructors for the new school year, but both instructors we’ve had have been experienced and very good at working with him on his level and following our behavior plan for him. He really enjoys going.
The other option that I know of is Aquakids, which is in Flower Mound off of Cross Timbers. They have one instructor in particular who is good with special needs. But their programs are pricey, and I’m not sure they cut parents of special needs kids a break the way the Coppell Y does.
There are some other options for the summertime, I know that Lewisville Park and Rec will do 1:1 at the same cost as group lessons but only if you call and specifically ask. Also, there’s a college student whose father is the LHS Swim Coach, and she teaches private lessons in her backyard pool in the summer. Her name is Kelly Gargan. But those are summertime only.
There is a Special Needs Service Provider Directory online at: http://lisdseptsa.txpta.org/index.php?module=dynamic_page.... You can download it or request a hard copy.
Also you may want to let her know about SEPTSA’s BigTent email list, since the general listserve is often used for questions and sharing information just like this. She can sign up at this link: https://www.bigtent.com/groups/septsa