Excellent! I'd start with 1/8 tsp of Miralax mixed with one tsp of water twice a day. If that doesn't make her poop soft enough, it can be increased to 1/4 tsp of Miralax with a tsp of water, twice a day. I wouldn't use the Lactulose once you start the Miralax, as the latter is a replacement for it. If you want to mix the Miralax with more than a tsp of water, that works too, just as long as she drinks all of it. Treats can be crumbled into the water to entice her to drink it. Or the mixture of water and Miralax can be stirred into her wet food.
That is good news about Trudy! To add to the above, if you have any of the foil packets of liquid/stew/broth/soup treats, Miralax can be mixed directly into those as there is enough liquid to dissolve it. Don't use it dry or sprinkle it on her food, even wet food.