You can find in Lightroom the photos a customer has chosen by copying the order's image list.
Copy the image list
1. Go to Client Galleries / Orders and open the order.
2. Click the ⋮ menu (top right) and choose List of photos.
3. In the List of photos window choose how you want the photo name (File name or Image title), the separator (comma-separated, semicolon-separated, space-separated or one per line) and whether to include the extension. If the order has several products, you can turn on or off the ones to include.
4. Click the copy button (top right of the list).
By default the list uses the image title, separated by semicolons and without extension. If you want to filter by file name in Lightroom, choose File name (and turn on the extension if needed).
Filter in Lightroom
1. Open the customer's session folder or collection in Lightroom.
2. In the Library filter choose Text and, in the drop-downs, File name and Contains.
3. Paste the list in the search box: only the chosen photos will be shown.
4. Save them as a collection so you don't lose them.