I don’t have any input into the Musical Theatre part of your question but I can add some input into the “park naturalist” idea.
A park naturalist would need some sort of background in natural sciences - wildlife biology, environmental science, botany, forestry/natural resource management (both of which include a wide variety of classes in specific natural sciences - botany, wildlife biology, entomology, dendrology, hydrology, etc).
An Outdoor/Parks and Recreation degree might be useful, but I believe it is less science-y, and more devoted to teaching the administration of outdoor recreational opportunities, not teaching the science of nature.
So your daughter would need to consider whether she likes the thought of being involved in the administration of outdoor recreational activities (hiking, boating, camping, etc), or teaching people about nature (trees, birds, insects, wildflowers/plants, wildlife, etc).
A history degree would not be relevant for any “nature” oriented careers, but would be helpful for employment with state and federal park service. The US National Park service administers not only parks like Yellowstone/Yosemite, but also national historic monuments, sites, historic parks, military parks, etc. https://en.wikipedia.org/wiki/List_of_areas_in_the_United_States_National_Park_System
These positions usually require a history degree (or something similar) and because interaction with the public is a primary job requirement, someone with a theater background would most likely be very comfortable with the job duties. Some of the sites are indoors (President’s homes, etc), others cover large acreages and have an outdoor setting (Gettysburg battlefield, etc.) with the latter types possibly being more appealing to a lover of nature.
Hope that helps.