Using iMessage when swapping physical SIM Card

Hey all, specific case here:

1. When I swapped to a DATA ONLY eSIM card on a recent vacation, I was able to use Messages (most of the time) because Messages (or so I was told) is tied to my phone number. So Messages still worked EVEN IF someone sends me a message to my phone number, EVEN IF the Cellular Phone service is not connected (Data ONLY Plan for international travel).
2. Now my daughter is going to Europe and her school program says she must swap out the PHYSICAL SIM card for one in the other country, in order to have a LOCAL Phone number. So the question(s) include:

• • Can she still use her Apple ID email to use Messages with a Local SIM card installed?
  • Will she still get messages sent to her US Phone number?
  • Or will that connection be "broken" once she logs into her Apple ID to get all the other "stuff" working on her phone?

I am honestly thinking of sending her to Europe with an old iPhone for the Local SIM, and getting her an eSIM for her current phone to use Messages, Facetime, etc. without losing anything.

Thoughts and recommendations are appreciated!