Hi INFJmom
welcome to the Apple (user-to-user) Community.
Re: "photos as attachments, not embedded. How can I do that?"
Am no expert in this area, yet your question surely deserves a response.
Wondering if we are talking about just a few photos, the occasional photo, or whether you have a lot of photos to send to your sister,
also
which device, (or Mac) you sister will receive the photos on.
Photos can be sent via eMail, or on the Messages app between devices.
Different eMail providers (Yahoo, Gmail, etc.) may handle attachments differently.
Lots of photos could be put on a small USB stick and sent via the post al service if that helps.
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Seems selecting and adding more than one photo at the same time can help send them as attachment rather than embedded.
Add email attachments in Mail on iPhone – Apple Support
says:
"Depending on the file size, the attachment might appear inline with the text in the email or as
at the end of the email".
and
"If your file exceeds the maximum size allowed by your email account, follow the onscreen instructions to send it using Mail Drop. See the Apple Support article Mail Drop limits."
Hope something above can help.
All the best :-)