Isabel lake was probably named by Albert Hale, The first Forest Supervisor of the Wenatchee National Forest in 1908. I was told by one of the editors of the Wenatchee World newspaper, who also lives in Albert Hales' first Forest Service House in Wenatchee WA, That Albert named lakes in the mountains after his girl friends. The girl friends part of the story may be embellished as he was married. He did name a lot of lakes after Women though. A review of a current map of the Wenatchee National Forest confirms that.
He was a topographer mapping the Cascades of Washington between 1897and 1907. The area was unexplored and natural features did not have names so he began putting names on lakes and mountains. His prolific place naming was due in part to Gifford Pinchot, the first Chief of the Forest Service.
At that time the national forests were relatively new and often largely un-mapped and lacking in place names. In order to better protect the forests from wildfire Pinchot felt it was necessary to have names for natural features and detailed maps so that fires could be located by name and fire fighters sent to the right places.
If the owner of the Searey is able to repair and fly it again it would be fitting to name it "Isabel"
Read about the names he gave to places in the Washington cascades and who they were named after.
https://en.wikipedia.org/wiki/Albert_Hale_Sylvester