iframe converted from https to http

I have an iframe that embeds a google map. The map link is https, but the page serving the iframe is http (see here: https://www.edithwharton.org/visit/hours-admissions-directions/).

Problem is that this plugin rewrites the iframe source from https to http, and I don’t want it to do this. Here is a discussion on the subject: https://www.ads-software.com/support/topic/this-plugin-breaks-embedded-google-maps-2014

I have added the jquery, which partially resolves the issue. However, I would prefer it if this plugin did not rewrite the source at all. Is there a filter or action I can call to tell this plugin not to rewrite this url? Or can you add something in the settings so that I can specify that this url should not be rewritten?

Thanks

https://www.ads-software.com/plugins/wordpress-https/